77 el camino classic

Do i need to drop the thm 350 to replace the 1-2 accumulator o ring??

first of all, my Haynes/GM THM350 rebuild manual says:

"Do not remove the Teflon oil seal rings (from the 1-2 accumulator piston). If they are damaged, replace the piston assembly. "

That being said, you should have enough room to remove the cover, spring and piston.
If its a bit tight, just place a jack under the tailshaft, remove the trans crossmember and lower the jack a couple of inches.

Thanks for the info. Do you know where I can get the O rings??