I went with MT90 when I put in one of Darryl's rebuilt transaxles 22,000
miles ago.  No leaks, shifts fine in all temps (teens to what we in
Southern AZ call 'teens' --- i.e. 110's).

I have used water wetter in other cars but held off on the Westy as it
seems to find any possible leak.  On other cars this is okay, you just
fix that leak but I wondered if adding it to the waterboxer would hasten
the leaking of the heads.

Geo Hahn
84 Westy
Mt Lemmon, AZ