The pump can be rebuilt if you have a replacement diaphragm. As said above it's not hard but requires some time and effort..grind off the rivet head, remove top plate and diaphragm, drill and then tap the shaft, install new diaphragm and little bolt/washer to fit.
I have diaphragms I will sell $10.50 including mailing. They are viton the best material to use should last another 30 years.
I have rebuilt about 6 of these..only one leaked..because I didn't flatten out the top plate(I bent it taking it off..only made that mistake once) the rest are working fine as far as I know. The good part is once they are rebuilt you can replace the diaphragm easily.. of course you shouldn't need to for 30 years.
If you want to try it I can give you the specs for the tap and bolt to use. It's best to have a drill press to drill the shaft..must be straight and it's a small shaft. I have been charging $45 to rebuild..you send your pump and I send a replacement..or rebuild yours, up to you.
New one at western honda $75 plus shipping