Cabby cutting out after 5-10mins then nothing! just clicking

Hi, bought my second cabrio on Friday, this one's a 85 GTi with 70k mileage full service history etc etc and no rust at all as far as I can see minus a tiny bubble on front wing.

I went to look at it on Thursday and he took me for a test drive, car was warm when I got there as he'd diven home from work, and it drove fine for 15mins or so.

Picked it up on friday, drove it to a friends house, then drove home about 45mins later, all fine again. Saturday morning went out to clean it and started it up but battery was flat-ish (but dash lights were working). Jumped it with my starter pack and all good, left it running for 10 mins then it cut out. Got in the car to try start it and nothing, just a clunky noise, no tickover, not even trying to start.

Yesterday my dad went out to drive it and it started up fine, warmed it up as we always do before driving, came back out 5 mins later to drive it and it had died and same problem…

I've read up on here but it seems everyone seems to get it trying to start but no fuel. My od cabby had the fuel starvation where it would die after 30mins which was the pickup blocked but this is weird that its 5-10mins then not even trying to start?

People have said WUR, Fuel Pump/Relay, Injectors but this seems to be on threads where it actually is trying to tickover, mine just does nothing, like the battery is completely dead so no power to start but its got charge in it and has only recently been changed by the previous owner.

Any help appreciated guys

Craig

A common problem is the fact that the starter is close to the exhaust manifold down pipe.
I had the problem that my car would drive fine and start from cold.
But when it was warmed up I could turn off the engine.
Then it would not start, turned out to be the starter motor apparently it's the haet that affects them breaks them down.
I replaced mine and not had aproblem since.

not sure if that helps.