[KobaltBlau]

In addition to the potentially hard to find Mystik, Chevron Delo 80w-90 is another high quality non-synthetic gear oil that you should be able to get. They also tend to go after the "Diesel" market.

However, there is an important difference between the Delo and the Mystic. The Mystik is suitable for "Service fill" of limited slip axles, where the Delo is suitable only for "Top-up" of limited slip axles. This means that you may need to add some limited slip friction modifer to Delo. This is easy to find, there is even a ford version, but you should not add more than .5%, half a percent, according to an expert I talked to. The danger is with the porsche balk ring synchros in a 901 or 915 box that too much friction modifer prevents the synchros from working well because they don't have enough friction. Another alternative is to add 10% dow corning molykote M, like steve W does on this board. He uses it with a Redline 75w-90ns synthetic, which does not have a friction modifier. I think the moly may help his LSD not chatter.

If I were you I would probably find the Chevron Delo 80w-90, put it in, and if your limited slip chatters (if you even have one) add .5% friction modifer. If you don't have a limited slip, then all you have to do is get some Delo.

Best Regards,