Yup, as suggested - water ingress into the compartment that houses the ECM/TCM, etc. There is corrosion on the pins, which is a PITA to remove - but already after an hour cleaning it - I reconnected everything, and it's working 'much' better. Reverse is still intermittent, so I'm going over it again. Could the tranny 'reset' (pos 2, hold accel 30 sec, then brake 10 sec, then start) help with that, or is likely still the corrosion?

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2002 X5 4.4i sport/NAV/ski - upgrades: electrochromatic mirror, aluminium pedals, tinted front windows, 20" rims, //M wheel w/ paddle shifters, CarPC (CarX)