Having trouble getting selector into park all other gears OK... no evidence of slipping trannies been working fine . Going is still strong etc

Just need a flush , change of filter and transmission oil?

Anyone else had this specific problem ...what was the outcome?

It might be as simple a change of fluid and filter.

Your trouble may also be caused by a damaged parking pawl - do you put the selector into park, and then let the handbrake take up the weight of the car?

could be

a broken engine mount

at the gear selector on the box
that cable may have an adjustable thread
slacken or tighten until you can select park and all other gears