Indeed Mike,
Electrolytic capacitors "drying out" is a common issue in valve amps and class A amplifiers due to heat but I hadn't expected to encounter the same issue in an ECU. I guess the ECU does contain a series of transistors and does heat up as a result but I know little about teh failure modes of electrolytic capacitors.
The main thing I can suggest however is that if any of you have an ECU and intend keeping the car I'd get the capacitors replaced before they start to eat the PCB tracks or show visual sign of failure. Whilst sourcing a replacement ST205 ECU may be a fair bit easier than a ST185 RC for the sake of around 40 pence of capacitors and a good drink to a friendly electronics nerd it is worth doing.
IMHO the most difficult part is trying to idnetify where the now non-existent PCB tracks should go! I'm hoping mine is still OK on the PCB tracks but it is still a PITA to try and trace the double-sided PCB tracks, especially when you have leaked electrolyte over the board.
I ended up using a garage LED inspection light under the PCB to trace the tracks and checked continuity with a multi-meter. You can clearly see where the tracks have been eaten.
Untitled by
diceman2002uk, on Flickr
Big thanks to Chris on this; without his write up and help I wouldn't have diagnosed or attempted repair.