I bought two undecs from the first order ,thanks to articles (postings) about problems with the F40s I test ran both of mine before buying.The first one was typical KATO,it ran smooth as silk.
The second one did not run "but" applying the slightest bit of downward pressure and it ran just like the first one.We removed the shell to discover the motor was half out of the saddle.I pressed it back in place ,test ran with out the shell,then with the shell.Yup just like the first one smooth as silk.
Sold both units early this tear,test ran both of them and they were still running sweet.
About the motor saddles, if none are available maybe putting the saddle in HOT water for a few minutes then weighting them down till they cool might help.(just a suggestion)