Starting issues

I know this issue has been raised so many times, but here goes.
I have an '83 all White Gti Cab. I have owned this car for 38 years. Totally standard no modifications to the engine, or any of the systems i.e. electrical, fuel or exhaust. The car has developed a problem over the last couple of years with starting (due to the use of other cars it has not been used, but kept on trickle charge and started every 6 months or so) But over the last year it wouldn't start at all. Played around with different fuel pump relays, some would buzz when the ignition was switched on and some don't only the sound of the relay clicking. Anyway to cut a long story short, playing around with Thermotime switch connections, cold start injector plugs, coil connections, the car started. It ran like watch from cold all the way up to normal running temp. I let it idle for around 5 mins. Switched off the engine. Would it restart? no way. Left it for about 2 days before i had time to get back to it again. Turned the key, started first time. Again running like a watch. Carried out the same procedure, switched off the engine, waited about 10 mins. tried to restart. Not having any of it. Does anybody have an answer or recommendations?