What is actually wrong with the winches you have now?
Winches should be disassembled, cleaned and greased/oiled every year or two, depending on use and exposure. Replace pawls/springs when needed. I have two electric Harken 66s, one electric Harken 44 and one manual 44. I can do the full servicing on all of them in an afternoon. I can just pull the barrels and lube them all in 20 minutes. If there is a problem, its probably because so many owners just run them until they break.
The boat is new to me so I haven't really had a chance to see for myself (haven't even sailed it yet). The winches work, but the rigger said they are a bit stiff and recommended replacing them. As I mentioned, there are 3 different brands among the 4 winches. I think Arco part are hard to find (from what I've seen) so I will probably replace those at some point regardless. I'll have them serviced and then see how it goes. But as I said, I think eventually I'd like to have all four winches from the same manufacturer.