I have an A4 which regularly, over the past few years, has become a bad
starter.

1.8 (110,000)

Engine turns over well but won't fire.

Can't see any pattern - leave to stand or persistence seems to get it done
but Missus not very happy.

I think a cure would be better than a trade-in (and cheaper).

Non-VAG garage says he can't find nothing wrong - any ideas?