focus (mk2) st tailgate lock problem

I have a bizarre problem with the tailgate lock on my (new) Focus ST3.
The problem is that the garage (dealer) can't fix it. They can't even get the problem to repro. This is _seriously_ intermittent.
The problem is that every so often, the tailgate won't open at all. Walk up to the car, unlock it via the remote as per normal. Pressing the microswitch under the tailgate... nothing. Nada, Not a sausage. No clicky noises, no apparent action at all. Anywhere from 30 minutes to several hours later, you'll find it operating normally again. The dealer HAS seen it failed _once_, but by the time their mechanic gets to look at it, the damn thing is always working again.
They did say there was a known problem with water ingress and took it in to look at that. They broke and re-made all the relevant connectors "greased" where necessary (I assume/hope they mean silicone), but reported no water found, and couldn't fault it.
This morning - failed again. But I can't take it back to the dealer because I need the car today and tomorrow.
This is driving me nuts. I gave up the RX8 because I needed the practicality of a hatchback - and now I've got a hatchback I can't rely on.... Arrrgh. It's doubly annoying because the ST doesn't have ANY way to unlock the boot except via the remote. There's no mechanical backup I can use if I've just driven forty miles to a golf course and can't get my clubs out.
Any ideas anyone?
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contacts as it will form a thin non-conducting, glassy polyoxysilane film after an indeterminate time. Better to use petroleum jelly (Vaseline)
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