So I am looking through your posts and I start to wonder if the Health of your machine is the issue here....
And specifically the health of the "Y" Gear Box and the two 685ZZ Bearings. I know it usually takes about 250 cut hours to wear out the bearings in the "Y" but it can happen faster depending on the carving and cutting load. More "Y" Stress, More wear....
I would find a source for the 685ZZ Bearings and order some. You use them 2 at a time. With the Tightening and Loosening of the "Y" Belt Posts it had me wondering....
When the bearings fail they let the belt Pull the "Y" Gear into the U shaped metal frame creating resistance and causing a stall. It also makes rub marks on the plastic gear, see picture... IT also wears thin the shaft as seen in the picture. In the past LHR sold the gear now they sell you a new gearbox.
I believe this is the root of your problem....
Just a WAG from AL.... Wild AL Guess...
Just one source of the bearings.
http://www.vxb.com/SearchResults.asp?Search=685zz
The reason the Y Gearbox in the picture 4 has a screw hole on top is that it is a former "Z" Gearbox... We had a bad run of "Z" Motors and encoders in 2007 and I pulled the gearbox off the bad "Z" Motors. This was before WE understood the wearing of the 685ZZ Bearings....
NOW we recommend PREVENTIVE Maintenance and replace the two 685ZZ Bearings AND the 2 Cut Motor Brushes at EVERY 250 Cut Hours.