Strange Wiper Fault

Anybody had this before or know a solution?

Basically my wipers have stopped sweeping all the way to the A-post and instead stop about 4 inches short. I assumed the drivers side may have skipped a tooth on the sprocket so I took it off and mounted it a little higher, but weirdly it still swept to the same point. I took it back off and mounted it back where it was and then it swept even less!

Two things have happened which could possibly have affected it, one being I have fitted a new rotary coupler / air bag squib that I believe came off of a 200 (mine is a 197) but I very much doubt this is at fault. Two is that the wipers automatically operated when my screen was badly frozen up a couple of weeks ago, which is why I assumed it may have skipped a tooth.

In any case whatever I do I can't get them back to the original sweep, which is massively annoying!

Can anyone shed any light??

Thanks, Rob
 
I don't think anything has seized up though, they sweep smoothly and quickly without any delay, it's just the sweep area is slightly less than it used to be!