23C
They are pretty rugged.
I have one of the old gray ones that I bought in the late 60's. Nothing has ever broken and, other than infrequent cleaning and a little lubrication, tightening some screws, and realignment, I have done nothing to it. I have no problems with it.
I also have a color head for it that I got in the mid 70's that I don't use anymore. It is the "new" blue color. Other than it needs a new lamp, I never had any problems with it either.
The Beseler products are very well built. The only things I have replaced were the enlarger lenses - both Nikon. I got a better quality 50mm (also Nikon) and the 80 developed fungus so I had to replace it (also with a newer Nikon).
The 23C isn't the state of the art and it isn't the prettiest I have seen but it is hell bent for stout and, for its price, delivers solid value
Dan