For:
#2 - Maybe the water drains are clogged. You can use some long steel wire and try to slide it through from top to bottom.
#3 - I would try the easy stuff first (which might be the correct solution): you might want to change the ATF & filter. The code you posted P0735 happens when you have one of these conditions: ATF low level, dirty ATF, shift solenoids issues, other mechanical problems, electronic issues.

If the filter gets clogged (old), you get low level ATF symptoms, which would fall in the: dirty ATF & low level ATF (because you starve the tranny).

Just follow the Bentley for this one, it's not very difficult. Be careful to have the 35-50°C temperature (trick: when the tranny has the same temp as your hand, you are at around 37°C - from this point, it will heat up pretty quick to 50°C - that's when you top off your tranny).

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Stable: e92is, e46 M54B25, e83 N52, e53 N62 - sold, e39 M54B30 R.I.P.