Hi Mudd,
Yes, don't add anything to the oil, saying that, you do know that the trans uses 30 wt oil, not 90 wt gear lube? I say that as I had no idea until I had to remove the trans/OD and replace the piston, rings, and liner due the DPO's use of 90 wt. The clutch was jammed so hard it had to be pryed apart...
Also, and you might look for this, mine had a warped rear housing on the OD due to the wreck it had been in. Apparently the trans locating rod/bushing can warp the case if the shunt is severe enough. The engine/trans has so much movement on the motormounts, it will bend the front frame crossmember too. I was able to chuck the case in a lathe and true up the fit without removing too much material. It went back together fine, and now doesn't leak.
Where is yours leaking from?? I know the drain plug on the OD is famous for leaking, but that should be able to be fixed readily. Otherwise its the seals or the case gaskets or ??
Hope this helps....Jerry Rude
BJ8/Lotus Europa TCS