For 3 years I own a 1994 E32 730i w/ M30 engine and Getrag 260/6 manual gearbox. In the past, I had for 10 years a 1986 E28 535i which also had the manual Getrag 260/6 gearbox.
Bottom line, I have 13 years of Getrag 260/6 experience.
When the weather is rather cold (e.g. below 18 deg. C / 65 deg. F), shifting becomes difficult on Getrag 260/6, particularly 1st to 2nd gear shifts. If you put ATF oil in the gearbox, shifting effort at cold improves a lot
However, when outdoor temperatures jump over 32 deg. C / 90 deg. F and the gearbox gets hot, the ATF oil will make shifting hard (particularly shifting into 1st gear from a stand still), and the gearbox may sound harsher.
Therefore I recommend gearbox mineral oil (85W, or 80W90, or 80W) at all times, except maybe in the winter. Although, even in winter time, if you are gentle with your shifts until the gearbox heats up, the mineral oil would be just fine.
Since I doubt very much that Getrag redesigned gears and/or materials inside the 260/6 in order to cope with the specs of ATF, I strongly believe that ATF oil was specified instead of normal manual gearbox oil just depending on the climate of country of destination. Therefore, you may want to play a bit with gearbox oils until shifting matches your taste.
Just make sure that you don't put API GL5 oil inside, because it contains sulfur and will damage the synchros. Also, stay away from synthetic oils, or you may enjoy oil leaking, particularly from rear seal (ask me how I know).
Last edited by RobertRO; 03-21-2018 at 10:12 AM.
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1994 E32 730i M30 manual
ex- 2006 E86 Z4M Coupe
ex- 1986 E28 535i
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