Thank you all for the excellent advice.
I have found and solved the problem...
It was the Bowthruster after all. A build up of carbon dust from the brushes on top of the commutator bridged up to the top bearing housing. I stripped down the whole top section, removed the brushes took off top brush holding part. I could then access the commutator and even vacuum out by the magnets. I polished the commutator with 1200 grit and scraped out the grooves.
Anchored Patmos, with pleasant 10-15kn wind.