Nope, no "inherent"problems, great boats. My guess is somewhere between 2005 and 2008, which is when they also ended the C34 & C36 runs and started designing and producing the new "5" series.
There should be an association, try
www.catalina28.org or a Google search.
Other than the wildly successful C30, this was the smallest boat Catalina produced with BIG BOAT features and systems. Some have mentioned that they think they tried to fit too much into too small a hull, but others love the concept.
If you get a Universal engine, the C30, C34 & C36 websites have a tremendous amount of information on them. Yanmars not so much, I forget what engines they used in the C28. If it's a Yanmar, do research on exhaust elbows, a recurring issue that is really maintenance that too many skippers ignore at their own peril. Kinda like chainplates!
Good luck. Let us know what you find out by searching around.