Check out this thread:
http://www.peachparts.com/Wikka/M103TimingCoverReseal
by Robert Ryan:
A note on the 5mm hex key wrench
There are three 5mm Allen bolts that secure the distributor cap. The bottom one is tricky to remove, in fact it can be downright impossible without the correct wrench. I have found the ideal tool is to take a 5mm allen wrench (L-shaped) and use a dremel moto tool to cut off the short leg and the bend. Take the long piece and stick it into a 5mm socket. I have used this so much that I glued it in and keep it there permanently. You might stick some chewing gum into the socket to keep the allen wrench from falling out. In this photo there is also a 1/4" extension bar. The combination of these tools makes removing that bottom bolt simple.
