I would try a salvage yard...you could get the whole rear hatch for 500.00!....
That linkage could be repairable...or rebuildable...or it could just need grease....(read below)
what wore out on the linkage?
a gear, a bushing?...linkages by nature are not complicated and are very straight forward in design....
found this on another forum:
On mine (E46 touring ) the wiper has seized a couple of times over the 4 years i have had the car, each time the wiper starts to wipe very slow until it stops , , with the glass section up , i sprayed WD40 into everywhere i could get it to go in !!! (Rags at the ready for drips !!!!) and by morning , it had worked it's magic , i was going to take the tail gate apart and get to the motor , as i have seen these can be overhauled as they do seize up with rust , Touch wood , not had anymore bother with it , The WD must have got right into it , wouldnt be a bad idea to take the panel off and give it a good coating of spray grease with it running , so you get all the moving parts ....
Take it apart and LOOK at the mechanicals...it will give you your answers!...if its truly broken and in need of replacement, you will know by looking at it.
If the dealership simply adds grease to the assembly and it works, then charges you 500.00 I would have a cow!