Last check during monthly INPA self-diagnostic revealed that GB temperature been on the high side with average of 99c during idle and 126c after a few runs. Normal temperatures should be around 80c during idle and 110c max.
Mechanic have suggested to replace the gearbox heat exchanger as it may be blocked causing not being able to perform at optimum level to cool down the GB.
Stock E46 heat exchanger (water-cooled) can be further illustrated by photo below. Very efficient cooling but the down side is it may get blocked over time and no longer performs optimally which in the long run may damage the GB as internals are no longer sufficiently cooled. This may attribute to premature GB failure which happens to many E46s. Signs of overheating GB are obvious jerks during upshift/downshift and dark-colored ATF.
Apart from GB damage due to overheat, GB may also be damaged if heat exchanger is damaged causing mixture of coolant and ATF to be routed back to GB.
Mechanic suggested for long-term, the E36 heat exchanger (air-cooled) is a better replacement as it requires no maintenance and no risk of failing (unlike the stock E46 exchanger) since it's air-cooled. Even though being an air-cooled alternative, it maintains the same level of effectiveness in cooling of the GB.
The same air-cool engineering was applied on all E39. Photo of both E36 and E39 heat exchanger as below.
E36
E39
Total all-in cost for parts and labor is RM500, inclusive of topping up of 1L of ATF.
No photos taken during replacement as car was left at mechanic's while I go to work. Photo taken by udm68 shows removal of bumper. LOL