No way to get the casette reels to move neither in PLAY nor in FF or
REW.
Idler was slipping against the take up and supply spindlers.
Idler tire replaced. Situation improved but still not enough. Spindlers
now turn when no cassette is mounted, but still blocked with a cassette
in.

Spindlers turn gently (they are free to turn) when operated manually.
Force of the idler
against the spindlers is very low due to relative positioning of the
three elements: idler, takeup and supply spindlers (a design
weakness...nothing can be done about that!).
My impression is that the white spindlers plastic has become too hard
and thus slippery. Something has to be done on the spindlers' plastic
to get the idler grip again...

Right? Any tip??

Thanks in advance.