Power lock problem on 99 Jetta

I searched the archives and didn't really see anything related.

When using either the key or the remote, the car does not want to lock all of its doors. Unlocking is (usually) not a problem. Mostly, its just the rear driver's side door but I have seen this behavior on all of the other doors every so often. Unlocking and relocking sometimes will fix it, but the problem seems to becoming more frequent.

Obviously there are many things that could be causing this behavior: bad relays, bad ground, etc. But I wanted to ask the opinions of those more experienced here before I start the frustrating process of troubleshooting the electrics.

Also, is it normal for these cars to eat brake light bulbs? I am replacing these about 4x per year on each side.

Thanks in advance.

If the vacuum pump runs long I'd suspect a vacuum leak. Are you using a good quality bulb? Cheap ones can be very short-lived.

Thanks for the reply. Vacuum pump is not running long as far as I can tell. Would it be possible for the motor to be failing, even if the car unlocks fine?

Bulbs have been whatever the autoparts store sells me.

Thanks again.