Most important is to check trans fluid levels with the motor running and warm.
Does the lever do anything in the 2 or L positions? With the 3pin triangular electrical connection removed it becomes a 3 speed manual with L being 1st, 2 being 2nd, and D being 4th. If you can get this working then it's likely an electrical issue, if not it's likely mechanical.
Do you still have reverse? This is usually the first to poop out.
And yes strawberry milkshaking is an issue, worth checking the trans dipstick for this. If it's clear then you're ok. Usually there is more water in the trans given the long time for the radiator pressure to dissipate.
How many km/miles on the clock?