Then they're probably slipping somehow after you're adjusted them. Best solution is to ditch them and get an electronic set-up, cheap and will retain the timing indefinitely.
You need to grease the plastic points cam follower with either A) magic NLA Bosch distributor grease if you are a USA Samba.com resident/inmate. B) ordinary grease if you read the VW service manual and take heed. The problem can be that the distributor cam can get grooved and shred the points follower (with dwell/ timing issues from the metal wear too) or the plastic is bad or there is no grease. Its meant to wear away at the same rate as the points burn down. In that case where the follower wears , the points gap will reduce. Alternatively if the points gap increases it can be that the condenser is failing and its causing the points to burn away faster with arcing. Most of these can be cured by using electronic ignition modules, but it is even better to also keep a second working distributor ( like an old one ) all set up and timed with the clamp fitted so you unbolt a faulty one, drop the spare one in, wire up and continue.
I had thought that and have been googling but can't seem to find any electronic ignition modules for my 111 905 205T dizzy
Are you using the correct contact set? As you have an all vacuum distributor the lead should come out from the opposite end to the contacts and a have a straight push on terminal. Fitting the later contacts with the flag terminal restricts the baseplate movement. You won't find an electronic ignition listed because the points cable goes through the bottom of the distributor, but you can modify the distributor by cutting a slot in the side for the electronic cables.
