Hard to find fuse!
After a week of searching, a friend of a friend with a an early '82 380SL let me pull his speedo....I found the same fuse, but his tested fine. After much searching I found that the fuse is a Wickman (has a small w on it), but cannot find out what circuit it protects (cruise control???). When I get a chance, I'll pull it and see if my odo stops.
As for finding one in the US, I found one company that stocks it, but has a $50.00 purchase min. Too much to pay for a fuse.