No, you do not need to disassemble the transmission to replace the reverse shift lever oil seal, heck you don't even need to take it out of the car. Disconect linkage from shift arm, remove nut that holds shift arm on and remove shift arm, now the tricky part, remove the plastic seal retainer with a pick or similar tool (preferably with-out destroying it, if you do ruin it you'll need a new one to put it back together you can still get them from a stealership or online), now using your pick again remove the o-ring, install new o-ring and re-assemble. I will snap a few pics this aftrenoon when I am at the shop and will post them tonight, I happen to have an 833 disassembled on the bench and can show the finer details of the task.
