How often is this service recommended, and since there is no dipstick, how would I check the fluid level between services. '08 135i conv. E88, automatic 6spd.
This kit is intended for removal of the mechatronic unit from the transmission, it's not a drain and fill/service kit which we also have available sold as p/n 24152333907KT1. Service interval per ZF is 80,000km (50,000,miles) or 8 years, whichever comes first, There is no way to check the fluid level outside of getting the transmission oil temp to the recommended 30-40 degree C and removing the fill plug which is ultimately not worth the effort. As long as there are no leaks you generally do not need to worry about the fill level.