Robert11 wrote:
Lately, it won't heat anymore, usually, and what I guess is a
code appears on the display: "H98"

About 25 % of the time, though, it does work.

Everything is possible, but the first thing I would guess is a fault in
the control circuitry, but can't say where there.. :-| But the first
thing I would suspect are electrolytic capacitors. If u have an
ESR-meter, measure the ESR's of those el.caps.

What's a typical lifetime for something like this ?

Hmm...I've found Panasonic pretty high quality microwave.. As although
the quality has decreased a lot on most electronic devices within the
past 15 years, my friend has an about 5 years old Panasonic microwave
with no problems, and that seems to be pretty durable microwave. And I
have a Panasonic microwave too, made in the 80's, I got it a few years
ago freely, as broken. I repaired it, there were just a shorted
resonance capacitor and a blown main fuse due to it. It also seems to
be very durable and high-quality device. So I would think that yours is
worth repairing.