Gus,
So glad to hear you landed safely - passenger deserves kudos as well for being calm and helpful.
You might call Air Parts of Lock Haven
http://www.airpartsoflockhaven.com/contact.html as they may overhaul this instrument.
Personally I prefer the Shadin fuel computer
http://www.shadin.com/products/fuelflow/index.html which as you can see from the previous postings is certified to act as the primary fuel flow gauge via STC from Osborne
http://www.jlosborne.com/index.htm It provides significantly more information.
I'm not sure about UK regulations but I pretty sure that in my Twin a certified fuel flow gauge is required for flight. The version of JPI EDM-760 I have is not certified to replace primary instruments such as fuel flow, CHT etc. so unless the Shadin is working, my twin is grounded. My twin may fly fine but FAA would not consider it airworthy and that of course immediately invalidates the insurance. Thought I'd mention it in case your aviation authority carries the same opinion.
Hope this helps.