Swapping transmissions, what else to replace while I'm in there?

[psjr]

I have good transmissions to swap into my 01 740 Sport (220k miles) and 01 750 (125k miles), and will be swapping them both in soon.
Wanted to get opinions on what else to replace while the transmission is out.

1. Coolant block plate gasket and rear main seal - these are a pain (at least the rear main seal with the special tools involved) and I very rarely hear of them ever leaking - are either or both of them worth replacing? I always worry about new work possibly causing new leaks (if it ain't broke...)

2. Opinions wanted - I have a 3.15 LSD for the 750, have been debating whether to do it at the same time as the transmission to save some work, or wait for later to isolate any issues from each one.

3. I have Guibo, CSB, and every other driveshaft part and new hardware ready for the 750 - if I only do the transmission now, which of these should I replace now vs. wait for when I do the diff? I was thinking just Guibo.

4. On the 740, the new transmission is not tested, but supposedly OK with 147k miles. There is a warranty on it, but I doubt it would cover labor. The old transmission ran perfectly except for F drum failure (no reverse). Should I swap in the known good torque converter, although it potentially has 220k miles?

5. Any other suggestions on anything to replace?

[PiotrC70]

not really a while it's out, but back in... replace oil + filter. I'm more of a replace it while you're already in there guy but can understand the "if it ain't broke" mentality as I do the same from time to time. I've only owned my e38 for 3 years now and have yet to read someone replacing the rear main + gasket so in this scenario, I would say leave it BUT, if you see any coolant residue or oil residue, replace.

[psjr]

if replacing both takes 30 min or less and cost like 30 bucks why leave them regardless if it is leaking or not? they will leak eventually, and that means removing the trans again...i bet they look like they could be done right now.

Since it's fairly rare for them to leak ever, the dilemma is whether doing work on them now is more likely to cause a leak (bad part, damage from install or removal, etc.) than the chance of them leaking at some point in the future.

[Hueristic]

The harness o-rings f0r sure.

And make absolutely sure the filter is in real tight, try to pull it off if you can without much effort then get a better o-ring.