I did the ones on my E320. I also replaced the transmission mount while I was at it. It made a huge difference. Both motor mounts were worn out.

I followed the instructions I found with some searches on this forum. The right one was easy to clear. The left one was harder. I can't speak for the V8 though, might be tight. $455 doesn't sound "excessive" considering the retail price for the mounts and typical hourly labor rates.

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1998 E320 120K mi
1991 Miata 80K mi
2001 Ranger 109K mi