Had the same problem (95 E300D) eventually turned out the fuse holder had distorted through heat from the fuse contacts and result was that brass contacts moved apart slightly leading to intermittent and then eventually zero blower.

solution was to move fuse to another location and to replace all fuses with copper tipped ones instead of the alloy oem rubbish.

Not sure if you have 124 so this may not be relevant just thought i'd mention it.

Keith