A4 gremlins?

I've been having a problem with my '97 2.6 V6 A4 since about the start of
the year.
It dies at the most inconvenient times, freeway, in a roundabout.  Normally
restarts and may not reoccur for weeks!
Mechanic looked at it on 3 occasions, no fault reported by computer.....
Finally last Friday night it died - all dashboard lights flashing, including
low fuel even, locked in Park, even central locking locked! Managed to get
it off the road, had it towed to my service man.
It's got to be electronics right?  Is there one central chip to replace or
more?  I know he tried hot/cold on the EMC (?) to try and force it to go....
I'm in Perth Western Australia