1997 Harmon Kardon radio /cassette .. Repair info?

My radio cassette player in My 97 Saab 9000 with OEM hardon Kardon .setup 10 speakers with a large discrete amp under passenger seat.
A seriously expensive system.. back then 🙂 It has worked V well for decades. I'm happy with it's sound .
Really Not wanting to retrofit some Disco era Contraption with dozens of Useless to me 'features'. And sketchy sound.
But my unit is now going intermittent.
IE; Tapes work as normal, but radio (all bands ) makes dead silence.
Curiously IF I play a tape for a half hour then the radio section comes alive. again and typically remains useable for several months to a year.
Sometimes only for a month.... No idea as to cause
Very strange. ALL wirings /connections have been checked . Not a loose connection issue.

Anyone have a circuit diagram.. for the head unit?

OR at very worst.... a suggestion for a Simple elegant Euro style head unit?
Cassette capability is unlikely and Cd s' are dying out as well. SD /USB intrigues
But how does one access the myriad files tracks without a monitor screen?
Zero interest in linking a phone or streaming. That even possible ?
 
Ambient temp makes no apparent difference.
Radio function loss is sporadic. It Never fails when in use.. only... on radio turn on.
Might ? be the wee Source switching relay being recalcitrant. Might be an on off switch issue.. Dunno
Have used quality electronics Contact cleaner on it... unsuccessfully.

Have heard mention of the NYC Saab radio repair service. .. thank you.
But with repair fees and two way shippings etc (Wet coast of Canada).
A Fairly good quality New unit would be similar costs.