cujo8,
check this out:
----- this text taken from the following URL ---
http://www.novak-adapt.com/knowledge/sm420.htm When refilling your 420 with gear oil, choose a GL-4 rated oil instead of GL-5. The latter has a higher sulphur content that is mildly corrosive to the bronze alloy synchros of the this and many other transmissions that do not have composite synchronizers. StaLube and RedLine are brands to look for, among others.
We recommend that you select a conventional lubricant or a para-synthetic in lieu of the full synthetics.
--- the above text is from the above URL at Novak Adapters website ---
If those guys don't know.. then it isn't to be known.
Other good info. about the 420 there also...
hope this helps...
-W
