Well, I got stuck ito the 124 wiper transmission earlier this week using some of the excellent postings available on this forum. I've no idea why I was lacking confidence, it really wasn't that difficult.
Once I had undone the linkage, I was able to revolve the working mechanism by hand, and discovered what felt like a coarse spot at the midway position (when wiper arm would be pointing vertical). When I separated the housing, exposing the plastic gearing I found the root of my problem, so similar to other 124 owners.
The round white plastic gear was fine with no damage to its teeth. However it was a different story for the black plastic 'rack' that the white gear arcs around within. The centre section of rack teeth, about 6 in all, had been ground down to almost non existence, hence the coarseness at midway position.
At this point I realised that the small black bits that I'd noticed lying around inside the housing were in fact what was left of these ground teeth.
Any lubrication that had been applied when assembled by Bosch had now turned into a hard wax-like compound, and was only evident on the outside edges of the rack - none where the teeth mesh.
I then undid the 3 screws that keep the clamshell located. The 2 slides were in good shape, as were the steel wheels that run within. But once again the only lubrication was outside of the areas where any friction occurred, and had turned into the hard wax.
I was turning the white plastic gear & watching how the steel rod moves in & out of its slide - I could feel a little resistance. Out of interest I applied just a little WD40 to the shaft & slides, just to see what difference lubrication would make. My God, it was night & day - smooth as & no resistence.
The bottom line to all this is that I have to pay AU$200 (US$150) for a 2nd-hand wiper transmission from a local dismantler.
I will be dismantling the replacement & thoroughly lubricating the appropriate parts - not exactly sure what grease to use...I heard that white lithium grease may do the trick...anyone have any ideas?
Having performed this removal/dismantle of the wiper transmission, I cannot emphasize too highly the importance of checking out your lubrication - ok, you have to set aside several hours to do it, but it would be well worthwhile.
Cheers.

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Marc Whitting
Australia