Fault at third wheel. ( minute)
Clean and inspect all ( gear teeth and pinion) of the minute wheel under high magnification. There is a slight possibility of bent pivot or damaged pivot hole, enlarged pivot hole cause depthing and exacerbate the condition.
I should have mentioned that to become a "authorised service centre" companies had to install the recommended Swiss tools even if the tools already being used were perfectly good they had to be replaced. If my memory serves me well it was in the region of €50,000. Many experienced horologists just retired and who could blame them.
Here's my workspace ... Mahogany writing desk from the 60ies (same time period as me and most of my watches) ... "neo-vintage" modded by myself ... In a few weeks I'll move out to a new home where I'll have space enough to organise a specific area for "machinery" ... a drill stand I already have and a pad-printer I have just ordered ... later I'll probably get a lathe and a 4 axes engraver ...