Renault Cleo V Reg. (connector to the coil box)?

Every now and again my old Cleo won't start. If I toggle the small connector (looks like a miniature scart lead) on the edge of the box whilst turning the engine over, and hit the right spot it suddenly fires up. It'll run for a couple of days then it'll happen again; sometimes it just won't start at all and the battery runs flat. Then I'll charge up the battery and eventually it'll start again.
Whilst the engine is running I've tried manipulating this connector and all wires leading from it in every which way to try to get the engine to cut out, but it won't. So this eliminates a loose connection.
I've switched off the engine on arrival at my destination and refired it to ensure it still starts, then a couple of hours later it won't start again.
I've had the engine scanned and the fault keeps coming up with the crank sensor but it has nothing to do with that.
This problem baffles every techical guy Ive come across and all I'm told is that it's a common fault with these old Cleo's. Great help!
If it's such a frequent occurrence with these cars has anybody else experienced the same, and more importantly - anybody got any answers?