[Edyz7s]

I have a 1995 240sx s14 that was converted to manual. I did not do the conversion but i've been owning like this for 2 years now. I believe I have a s13 transmission since it does not have the s14 crank position sensor on top of the bellhousing. Also i believe it has the auto ABS driveshaft since it has ABS and its pretty long that i think it touches the end of the transmission (but not enough that it grinds on it hard). So ever since then it would leak around the shifter. I first replaced the output shaft seal thinking that was it but continued leaking. Recently i replaced the shifter gasket cause it had only RTV. So with both seal (replaced less than 10k miles) and gasket, it is still leaking transmission fluid.
I'm concluding from what I assume, having the wrong size driveshaft, its causing it to leak fluid from the output of the transmission.
But this is where it got worse.
Recently I installed solid subframe risers from Gktech because i am low. Doing so it helped greatly with my suspension and the geometry of the car. But I believe it made the drivetrain worse. It only happened on 2 occasions after installing the subframe risers, where it seems like the differential locked up or something. When I would come to a stop on neutral, something in the rear would lock up causing it to shake the car. I wouldn't think it would be the ABS because even after i let go of the brake it would shake under 5 mph. I just feel its all connected to the driveshaft being incorrect for my s14.
But my main question is, if I were to have driven a lot with the incorrect driveshaft, can it ruin the rear end of the transmission? I drove around 50 miles on the freeway recently and after that it left a good amount of transmission fluid underneath the car and it's never done that before.

Apologies for the long post, just trying to be thorough.