All models have the same mech no matter which version. There is a video on You Tube on stripping one down and putting it back together.
Plus google it and you will find how to disassemble one in pictures.

I would suggest you consider replacing the seals just for your own piece of mind there is a seller on that does all the seals.

The sliding sledge rail can seem strange and I have known guns that slide when they should not a simple push the barrel forward before each shot and they shoot fine, or load the gun with the barrel down towards the floor and all is sorted.

You can even google the serial number and find when yours was made which is a deffinately an SU model due to the adjustable cheek piece.
The left hander are factory made.