Poorly cutting C & H mountcutter

[Bigkat]

Hello One and All,
This is a new forum for me - but very interesting reading all the topics and comments !
I have a venerable C & H mountcutter, which has served me very well for over 5 years. I guess it has cut in excess of 10,000 mounts.
However, it has been stored (badly) for 2 years in a dry environment and now it is being pressed into service again. My problem is that it will not cut parallel, the first cut into the mount is correct - but by the end of that cut it is out by 1mm.
Doesn't sound a lot, but it does show in the frame.
I have cleaned and measured everything, using the original instructions.
I suspect the cutting head, which does rock slightly on the rod, but it has done this before, without the results I am now getting.
Every cut of every mount is exactly the same, the aperture looks and is, out of square with the mount edge.
I have checked the base board is flat and the cutting arms are square.
Anyone any thoughts ?
Many thanks for reading this !
Vernon

[JFeig]

the cutting arm is square.........but is the measurement arm square?

a quick check is to cut a board from the front and then the same board from the back............if the cut lines do not line up, the measurement arm is out of alignment.........the steel bar on the right that it rides on and attached with 2 scresw will then have to be adjusted.

[Bigkat]

Many thanks for your reply.
Have now solved the problem.
Vernon