When this happened to me I had to have it towed. Was only able to back into a parking spot. Anybody who has a W124 or W201 86-93 with 100 to 150k on the transmission really owes it to themselves to get this checked ESPECIALLY if you drive far from home often. It is not a pleasant experience!
ezra242 do a search this failure has been discussed before...I believe its an easier job for a tech who has done the work a few times before.