1986 325e lost reverse

[1974Torino]

Hi all. My gf's 325e lost reverse just this morning. Goes forward ok, I can feel it barely lurch when it goes into reverse, but it just revs like it's in neutral and makes a slight whirring sound. The trans does seem to be on its last legs anyways because it's been late shifting for a while now. A couple months ago I did a fluid change (just drained the pan) replaced the filter and added some stop slip and that woke it up a bit. Is it worth digging into the trans to see what's wrong? Possibly a simple fix? I've got my eyes on a 93 325i 5 speed for sale that I'm considering buying to swap the drivetrain into the 325e, obviously that's a huge task but if the trans is gone and also the engine is weak these days maybe it's worth it. Anyone got any foresight on doing that? I have good experience with turning autos into manuals and I've done engine swaps/ls swaps but i don't have the most knowledge on bimmers.

[dworthy]

To make thing easier for the wiring if you do plan on putting a M50TU or M52 motor into the car, something like this will help: M52TU/M54/S54/S62 Wiring Loom Adapter (E30/E34/E36/Z3) - Hack Engineering

You can also take a look over at the Engine Conversions sub for more info too.