The later ones, built I believe in France, were actually a C series with different fenders. Make sure you take the serial number with you when ordering parts. I think it was a couple months early in 88 they did that. A dealer can tell you what shift built it on what day with the serial number.
If the transmission only wants to work one direction, chances are it can be fixed with a few o-rings. But it takes disassembling most of the machine to get to them.
They'll lift more than a 580 super M, if you can counter-balance it. Also better in mud. with an extand-a-hoe, you can balance it on the rear wheels, and walk through mud like you wouldn't believe. In one field we were tiling for a neighbor, I drove our 555B out to where my dad was digging (and stuck) with the 580SM and set up where we could hook buckets so he could move.
If you have to do a water pump, you have to tilt the radiator and oil coolers forward, you will not get it in place without goofing up the gasket otherwise.
They aren't as fast as a newer machine, but for the price, as long as it's fairly tight, it's hard to go wrong with one.
One more thing, if there's a "<" or ">" on the stick above the "full" mark, if you are going to be working a lot of steep sidehills, fill it to that mark, or it could starve for oil.