I too use that model Makita with my Gen 1 jig.
Indeed they do wear out, during my fourth lower it began to chatter, 5D said it was the bearings so they sent me two new bearings. They did not help with the chatter, it was indeed the end mill.
Recently I was able to find a new and better quality end mill on eBay, will see how it works in a month or two. Here is his eBay handle. americangunsmithtooling