The Scubastar is a clone of the USD Deepstar. It is a simple flow by piston design. If I remember correctly it uses the same generic seat as the Scubapro Mk2, Mk 3, Mk 200, Mk 2 Plus and it should be reversible, so you most likely will not need a new seat.
There will also be two o-rings that matter, the piston head o-ring and the piston stemp o-ring and both are also normal, generic sized, 70 duro nitrile o-rings.
The IP is controlled by spring pressure and is adjustable only with shims so put back in what you took out and the IP will be the same.
It is in short, dirt simple and intuitively obvious to service and a manual would not be required.