The gear selector seems to be stuck in P, but if I put a little bit of force I can get it out from P to D, however when I do this I can hear under the car noise from the transmission. Because of that like 200 kilometers ago I changed the oil in the transmission(ZF 5 HP 19) along with the filter, magnets and the bolts. It was pretty dirty the oil and it was looking that it needed to be replaced. I does not do it all the time no matter cold, hot but seems lately is doing more frequently and is an unpleasant. When I switch from other gears to park it goes very fine, the gears are smooth except the second gear it hesitate a little before the third gear, I can see in the RPMs of the car how it wants to shift but is delaying the shifting with about 1-2 seconds, however is pretty smooth. This is happening only <2000 RPMs if I accelerate after 2000> RPMs all the gears go smooth. I changed the oil DIY by myself if that matters with original ZF parts.
Other information that I know, I did check the transmission with ISTA tester/software to see if it has the same VIN as the car, and yes is the original gearbox acording to the tranmission computer. 235000 kms on clock. No errors/fault codes on the engine or tranmission.
I suspect the selenoids, the cable, the interlock shifter(it has some glue on some plastic parts), and lastly probably something is failing in the tranmission itself. Also I suspect the previous owner put some additives in gearbox to hide the fact that the tranmission has issues. The car had 1 owner, however I bought it from a dealer some time ago.
Where should I start to investigate?