So for the past couple of months my 04' auto 4-speed 8 has been giving me some problems. They all seemed to come at once:

So I hit my 8 on a few bumps (non-intentionally of course). And I was driving one day and experienced extremely a weird gear noise on acceleration and inconsistent throttle which at some points it wouldn't even pull. It cranked and turned over just fine This gear noise would get higher the more i accelerated, so I just kept it under 3k rpm and got it to my mechanic. He told me a bracket was broken above my midpipe, fixed that and i had some loose bearings fixed those all fine. Im at 38k kms mileage so i did a gearbox flush, but as soon as he took out all the old fluid it was black burnt and had a ludicrous amount of metallic gunk all over the magnets and filling the gearbox. He said that its the worst he ever seen.

So he just told me to drive it around as long as it doesn't give me trouble.

The only noticeable difference i've seen is I can sometimes hear the oil going through my gearbox, and don't know if it should be audible as it is. The gear shifting is not as smooth, and it feels like the gears won't shift as fast as they should.

I don't know to what extent its damaged and usable, although the power and torque seems fine. I don't want it to somehow affect my compression, indirectly.

Is it a common issue or not?
Does it affect the compression?
How can i check for addition wear beside checking the consistency on the dipstick for metallic particles.
Are the symptoms I'm facing typical for minorly worn gearboxes, or majorly worn gearboxes.