If you are calling that part number a "gasket" and not a seal, which it is, then I am assuming it might be best if you don't take the pump apart.
I'm not talking down to you, but trying to prevent you from getting into a repair
that might not turn out well for you.
As far as replacing the seal you have ordered, it was mentioned to remove it with the Sheetmetal screws which works well most times but one has to be careful to not damage the shaft or the bore it lives in.
OR
The housing can be removed by just removing the 2 hex bolts that retains it.
Of course one has to remove the drive coupling on the input shaft first for either procedure so the seal can be slid off it and the new one installed.
Then pay attention to put the housing back on the same way it come off--in other words paying attention to the milled flat spot on the housing (#55) it needs to go back on with the milled flat on the same side, if not it won't pump.
of course you should also replace "O" ring (#43) that seals the #55 housing to the hydro case if you remove #55 housing.
Also if you don't know, make sure the shaft is without burs around where the coiled pin retains the coupling so as not to nick the new seal.
Also a dab of grease in the center of the new shaft seal will insure that the seal does not start off dry.
Please understand I have no knowledge of your experience or lack of it.
