Wipers driving me mental!!

The front windscreen wipers in my 57 plate 110 are gradually failing. First I started to lose high speed, it would become jerky, stop then start again jerkily but normal speed and intermittent were fine. There was a rusty stain coming from one of the wiper bearings so I had that replaced and the linkages checked, that seemed to fix the problem for a while.
Then the fast setting problem started again and now doesn't work most of the time but occasionally will work but not at fast speed and jerkily. Then the normal speed doesn't want to park in the right spot and now the intermittent is no longer intermittent and just wipes continuously and parks in the wrong place.
I thought it could be the stalk, so i bought one from e bay and plugged it in but still have the same issues.
Is it the motor?

Two speed becoming one speed is likely motor problems,wearing out or just gumming up.

It's a bad idea to allow tratter wipers to get wet.

I suspect the rusty spindle. Either its happened again or was never really fixed the first time. Motor could be fine but the intermittent timer has been overheated as a result of the above.

Problem fixed. New motor did the trick. I now have both speeds and intermittent.
Thanks