The fit on these parts is not critical and the seal will seal pretty well even after 30 years unless severely damaged... and there isn't rally anything in strained oil that can do severe damage. You may still get slight seepage that lets the tank empty to the sump over weeks but is that a big problem?
The mechanism gets gummed up and a decent cleaning should have it in good working order.
While you have the pump out you can clean the screen at least, and disassemble the pump if you want. There aren't any internal parts separately available but you cen see the condition of the rotors and seals to gauge whether it needs attention. Someone here - Hondaman maybe? - was trying to find replacement O-rings and the oil seal between pumps but I don't know how that came out. The O-ring seals between the pump and engine are available at least.
All the O-rings are theoretically available but getting metric O-rings can be a challenge. There's a standard set of USA inch sized O-rings, set up for the WWII armament industry, so almost every inch O-ring used is one of the 400-odd sizes made standard. The metric world never did this and there are thousands of sizes used... all can be had but often one has to order a thousand or more when you only need a few.
