I bought new rubber from McMaster-Carr, spent about $85 on enough to do all the mounts, seems like it was 5/8" thick?maybe 3/4"? -- it was the correct width, I just had to cut each piece to length. I cut the metal plates off the old mounts using a razor blade & re-used them w/the new rubber. Used a hole saw to drill the hole thru the middle & simply sandwiched the new rubber between the OE plates.
