Hallo Peter,
I lost contact with you in the nineties. My 403 came back on the road in
1995 completely rebuild.
I had my 100A engine reconditioned by Gerrit Meijerink in Enschede. I can
give you their adress details.
They installed new valveguides in the head, new valves and hardened
seatings for unleaded fuel.
And afterwards they pressurised the head several times .
All other work to the engineblock was also marvelous . I have done since
1995 some 40.000 KM's
without engine trouble.
Please contact me off-line on 020-6413921 or jpkoopmans@xs4all.nl

All the best ,
Jaap Koopmans, Netherlands