See if the reversers in selfwinder module turn as you give it manual wind. Listen for sound from barrel as wind.
Mainspring's dimensions are to be measured to find a suitable replacement for the MS. Which I am likely to have .
I've got a Unicorn 1920s watch that I'm treating as a long term project as it has numerous issues and after cleaning the movement yesterday I discovered I had 3 cracked jewels that will need to be replaced and they are the bezel (rub in) type.
It is one train jewel and the two balance end stones, its even possible the cover stones are chipped too as I haven't removed them yet to check they are ok.
I've got the tools for opening up the bezel and still chasing a set of closing tools, but if needs be I could always make something to close the bezels.
Looking at Cousins they only seem to sell the modern friction fit jewels, is there anywhere that sells the bezel fit jewels or is it a matter of trawling Ebay for New Old Stock?
Since I believe that Rolex is a company that makes it very difficult for independent watchmakers to get factory parts, and this 2555 could have proprietary parts, some parts may be tough to get. However, if it's a mainspring for an ETA model, I'd be surprised if a watchmaker couldn't find one. Perhaps there's something else wrong with it that had the watch-person tell you that the part was no longer available. I suspect you could send it to Rolex/Tudor, but it would cost a lot of money to do anything to it at all. Good luck.