Fuel Gauge Problem**

I seem to be having a problem with my fuel gauge, now i have narrowed this issue down to the fuel sender unit. i went to remove the sending unit today to give it a check but with no luck on removing the lock ring. Does anyone have any tips besides the screwdriver and mallet technique?

My fuel gauge seems to rise on its own accord sometimes by as much as quarter of a tank, and im not convinced it goes back down to the right level after. I think the reason for this is because ive recently ran over a badger which could have possibly knocked it out of place? does this seem logical? am i looking in the right place for the sender unit - underneath drivers side rear seat (RHD model). Does anybody have any pictures of what the sender unit looks like as im looking at a couple on ebay but im unsure if they're the right part!

Here are the links:

Mazda RX-8 192 FUEL PUMP SENDER UNIT | eBay

MAZDA RX8 FUEL PETROL LEVEL SENDER UNIT SENSOR DRIVERS RIGHT O/S SIDE | eBay

Mazda RX8 petrol fuel gauge sender unit | eBay