Charlie - Is the filter the old style that mounts vertically on the side of the engine, or is the later type that extends horizontally from the back of the oil pump? If the former, only Moss or Abingdon Spares
https://www.abingdonsparesllc.com/ carries them. If the latter, filter inserts can be purchased at almost any auto parts store - Hastings P172, AC AC32, Fram CH814PL or the equivalent in any other brand. These filters are also used in the MGA and the early MGBs through around 67. The filters come with 2 or 3
gaskets. You want to use the gasket that measures closest to 0.088" thick. Make sure that the old gasket is completely out of the grove (a good light, mirror and dental picks are helpful) and that the new gasket is well seated in the grove before putting things back together.
If you have the filter that attaches vertically to the side of the engine, you can get a spin on adapter to replace it. It would cost about the same to purchase a spin on adapter from Bob Grunau (e-mail
cgrunau@pathcom.com) and replace the whole thing. Bob also makes a spin on adapter for the later engines.
Cheers,