It's been done.
I can't remember exactly, but from under the dash, you remove a series of screws and then pull the servo away from the bulkhead.
This allows just enough room to manouvre the old one out and the new one in.
Someone once did post some pictures, so maybe it's in the tech guides.
The item is listed as a Gasket on the Fiat system and costs about £18.00
If youre around the pontefract area, i have a new one, zinc coated and ready undersealed, which i never got around to fitting.