UPDATE

During the summer I got round to a little tune up. Fitted a set of H8DCs which were supplied by an aftermarket parts supplier in Dublin. They're in between the H7 and H9 I guess but importantly, they're not resistor. The car has been running very well since June, even now into the damp Dublin winters.

Over the holiday period, I'll have a look at the distributor to check for the verdigris build up that used to occur. Hopefully its gone! If the distributor is clean, then it will mean that my old idle problems may have been caused by resistor plugs causing extra corrosion on the distributor cap.

Will keep you informed.
Gerard