This is an APM 6" F/8 achromat. (TMB designed, but I don't hold the problems with this scope against TMB, they just designed the lens). Even after APM replaced the original lens, this scope never lived up to my expectation. It still has some optical problem that prevents it from showing a good airy disk. It shows a "C" shaped airy disk (this is not a cell collimation problem...Cheshire check says it is good). After waiting a year for APM to replace the FIRST lens, I won't wait another year for another one, and I am tired of playing with it.
The correction is actually good (better than 1/6), so I suspect that the problem is element spacing (wedged?) or centering or something. The lens has been handled (to try to rotate, change pressure, etc), and needs cleaning, but there are no scratches or chips. Visual color is actually VERY well controlled (TMB optimized the design for visual use.. It has less color than other 6" achromats I have owned). At anything short of very high power, it performs quite well.
The OTA is in very good condition overall, however the original paint was not well applied and there are a couple of tiny flakes. Still, it balances well, and is light enought that it can be carried on a mid-size mount. Rings are beautiful. Maybe you can troubleshoot it and make it perfect. The potential MIGHT be there. I don't think this problem is ground into the lens. The out of focus airy disk patterns look too good for that. Interesting trades considered. Non Astro items considered. PCP (or good springer), Classic Audio equipment, ??? Hard to set a price, so offers will be considered.