So if you are having plumes of white smoke coming from your rx8 after turning your car on and eventually stopping when the engine comes to temperature it may be that you have a blown coolant seal. There are many other threads of people who who have done some trouble shooting in the past, but I never got solid information on how stopleak interacts with a rotary engine. Below is a picture of roughly the severity of what a blown coolant seal may look like. Now in my case I ended up seeing about 10x more smoke, enough that I couldn't see across the street. Sorry, but my phone with many of the pictures I had of my pictures across the years I did this testing was destroyed so I will be using googled pictures that represent what I found.
Other issues potentially present:
-failure to start (coolant wets plugs>> fouled leading plugs leads to not starting)
-battery/coil/starter premature failure due to excessive cranking
-poor heat due to exhaust/air in the heatercore
-Low coolant levels, overheating issues (some higher mileage coolant level sensors don't work btw)

If we look in the engine, usually this will occur in the lower part of the engine between the sparkplugs and the exhaust ports. Here is an image of a broken coolant seal.

Now I experienced this with my first rx8
> Which lead to a failed rebuild (saw it was blown coolant seal).
> Which lead to purchasing a second high mileage rx8 to get through college, turning rx8#1 into a parts car.
> Which lead to another blown coolant seal engine both ~120k Mile engines.
> Leading to testing various bars stopleaks to get through college
> Engine lived until completely losing compression even at cold starts.
> Eventually leading to a successful rebuild now graduated from mechanical engineering.
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Now during college, when I needed a car and already was making long term plans to rew swap(still in planning), I figured I would end up using my second engine to test anything that I could. Since I had this coolant seal issue twice I wanted to finally see what stopleak would do. This also lead me to bring a low compression motor to its limits.

From forum rumors I looked at two Bars Stopleak products.

The headgasket sealer was my first choice since I saw a brief forum post about guys who had a race engine built that blew a seal right before a race and tried this in the engine and it held.

Following the Instructions to a tee, using about half the bottle for our 1.3L.
Side Effects:
+Constant coolant level
+Plugs lasted longer
+Could Survive prolonged high rpm over the course of 40 mins to an hour (spirited mountain pass driving)
+Lasted about a year of college(5k miles), through New england weather (even having fun in the snow)

-Caused a smell like burning plastic constantly
-Could visually see "crusty material" forming inside the coolant overflow tank. (pic below)
-Caused sludge leakage out of the relief hose, spraying all over my engine bay. Ruined power steering connector over radiator fans (fixed by hard wiring P.S. connection. Fixed spray by running a longer relief hose through my undertray to the ground.
-Heat nolonger comes from driver side this due to driver side of the heatercore being higher in the heatercore. trapped air from previous leak lead to stopleak reacting to that air and blocking the higher side of the heatercore. ( Fixed by running a pump in a bucket of water straight to the heatercore and back to the bucket, then changing pumping direction several times)
-Due to how the Rotary's coolant jackets work, there are many pockets where air/exhaust can become trapped inside the engine and take some time to work its way out. When the stopleak is first introduced it will react with these air pockets and cause pockets of sludge. For the renesis in particular I had a few pockets in the endplate irons and around the exhaust sleeves.

This is roughly what looking into your coolant cap would look like.

This is roughly what the sludge inside the engine would look like.
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Now the second Product I tested when the coolant leak started happening again was the bars liquid aluminum radiator stopleak. My thought was that the aluminum might bond better to the aluminum housings since the housings have the coolant seal channels in them.

This outright did not work at all, infact I believe it reacted with the sludge of the old headgasket stop leak in the system and changed the burning plastic smell to a burning dead animal mixed with rotten milk smell. Several and by several I mean about 20 or so coolant flushes later I did another round of the headgasket sealer to survive senior year. (another ~5k miles) Spent holidays/ time home tearing down my first failed rebuild engine and cleaning parts. While the headgasket sealer kept my second engine running.
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Now if you are considering using stopleak:

Don't

By the end of it you will end up spending more money trying to keep a dying engine running, than just getting a rebuild. Think of dropping 80$ in plugs every month. 300$ LS coil upgrade. 250$ starter upgrade. 250$ batterys each time you kill one. etc. Not to mention the amount of trouble caused by buying and trying to get rid of coolant+sludge. The amount of damage that will be done to your coolant/heating system will amount to more than it would probably cost to buy another rx8 beater>future parts car while you wait for the engine to be rebuilt. Or just a plain beater car to abuse through future winter anyways.

Unfortunately for me, my first self rebuild had failing compression and I ran out of time before college started to finish my build, my father also couldn't work on it much due to health issues. I had already spent the money on a rebuild and couldn't immediately dish out another rebuild's cost. New England isn't exactly known for world renowned rotary shops to trust....or even ones to not trust for all I know. By the end of it, during my engine teardown I found that I had entire pieces of my coolant seals gone in multiple places. Stopleak was solely responsible for holding up to 9k rpm pulls which was surprising to me......those areas were a bitch and a half to clean up during my final rebuild. By the end of running a low compression motor to its limits with a failing coolant system showed signs of rather cooked bearings and an ugly looking E-shaft.