1) go to a craft shop (we went to Jo-Anns) and look for a sheet of "foamy sheets" that measures 1/4" (6mm on the label) thick X 9" X 12" (or any other size) but 1/4" is the correct thickness
2) place the dome lid on the sheet; press down on the lid in order to make an outline of the lid in the foamy sheet
3) cut around the imprints
4) press the cut-out into the lid groove. You can get 3 or 4 gaskets from ONE foamy sheet.
Perhaps this procedure could be used to make gaskets for any food processor/blender.
The cost for the foamy sheet was $1.49
The 6mm (1/4") thickness fits right into the gasket groove.
We ran our unit on HIGH, with the container FULL of water and DID NOT HAVE ANY LEAKS! Good luck.
Hope this helps a lot of you who have this problem.