UPDATE!!!!!!
So... I sent my German BMW Zentrum(dealer) an email asking them to recheck their info for which gear fluid is needed for my 135i. They now say that BMW says Castrol SAF-XO is needed for all non m-cars. SAF-XJ for M-models (bc of the LSD). Even though on the parts screen I know I saw SAF-XJ! lol
So... I then contacted Castrol Deutschland's technical dept. They told me that... yes, SAF-OX is the oil for a 135i (and all non M-models) and SAF=XJ for M-models(bc of the LSD). But then I asked them why does all of Castrol's spec books say to use SAF-XJ in all of the BMW models. They wrote me back this:
Herr xxxx,
Many thanks for your email.
SAF-XJ can be used in both sorts of differentials, with and without the need of
a limited slip additive. SAF-XO is just for the use in differentials with
normal lock applicable.
So, with the use of SAF-XJ you will be on the safe side.
With kind regards
Deutsche Castrol
Internet Service Center
mailto:kundenservice@castrol.com
http://www.castrol.de
Fax 0800/ 999 27 26
...........
So... It IS safe to use Castrol SAF-XJ in our cars. I will use the gear oil I bought. The only thing is the thicker gear weight of the oil. I found some data tech specs online... and found out that the two oils (75w90 vs 75w140) are very close in specs.
Castrol data sheets
SAF-XJ
http://datasheets.bp.com/bpglis/FusionPDS.nsf/0/CB7FD8F52ECCEA20802577ED00480C06/$file/BPXE-85KPBQ_0.pdf
SAF-XO
http://datasheets.bp.com/bpglis/FusionPDS.nsf/0/32CA6B93186701BD802577ED004A99DF/$file/BPXE-85KS8S_0.pdf
BMW oe fluids pdf…
http://www.billswebspace.com/BMWOper...rive331108.pdf
Dackel