Got a mk3 vw golf, for the most part its fine, but every so often there is some form of glitch in the power supply.

The glitch causes the clock to restet and so does the radio (allong with all the preset stations).

This does not happen every time car is switched off.

The car starts without any problems and the battery never needs charging. The battery has not been disconected.

Any one got any ideas what the cause of the problem is?

I'm assuming your radio and clock come from the same source. Therefore, it may be a dodgy fuse contact... try taking out the fuse when it's on and replacing it, this way it cleans the fuse and eliminates it from your points where to look. Failing this it may be a chaffed wire (not yet through to earth) or a faulty connector. Use logic to track it down... failing that run a new wire from an alternative power source - cigar lighter for instance.

does sound a lot like a fault on the permanent live feed to the radio/clock, which is unfortunate as being permanent live gives more opportunity to short when you're not there.

as hellfire says, a feed from the fag lighter will work if its permanent live, and if not, a feed from something defo permanent live like hazrd feed/side light feed.

hth
tom

People are bad about loosening the straps to get a panel out then forgetting to snug it back up.

Had a friend whoose Chevy did the same thing. Popped in a new screw and all was good.