Like the Model 3000, the 1000 was made by Howa and also sold by Mossberg for a year or so after S&W dropped it.
The 1000 is not really a "clone" of the Remington 1100 like the 3000 is a clone of the Remington 870.
It's a very good grade shotgun. The only "problem" is that the neoprene washers in the gas system may deteriorate and need to be replaced.
These were very good quality guns, that again, just didn't have enough to offer over the Remington.
This part is from memory, so don't hold me to it:
The Model 1000 has a unique magazine block that blocks the gun to a 2 shot magazine to comply with Federal game laws. This block can be removed, allowing the magazine to hold more shells.
This is part number 39 "Capacity Reducing Pin" on the Gun Parts diagram.
You can buy new "O" rings from Gun Parts and LSG. I've heard some people use automotive "O" rings.
Gun Parts sells parts under both the S&W and Mossberg names: