I converted my TS 55 EBQ (2009) to take the dust bag using the "Festool-ET-Winkelstueck-TSC-55-REB" part number 10015824. It didn't fit properly. The diameter is marginally greater, and the "clock position" female indents did not match the male tabs on the saw housing. It is actually the tab positions that cause the non-fit, not the overall diameter. Unlike some other people's success with rotating the attachment until it clicked into place, this was not successful on my saw. Even though there was a "better" fit, there was no "perfect" fit. The issue was slightly different tolerances not of just where the tabs were, but how far away they are from the collar. 10 seconds widening each hole using a hand file is all that was needed. Total job time including opening the case, discovering the problem, using the file, putting it all together, was less than 5 minutes.
Opening up the housing of the TS55 was a good idea... there was all sorts of gunk hiding in there, and I could spot material that I had cut two years earlier! OK, so now I have to include opening up the housing and cleaning it as part of a regular maintenance cycle. TBH, this gunk is probably due to me sometimes using the saw without the vac. But good to know.
Recommended conversion.