Hi from WA

The 1980 one is larger.
I have a spare that needs a rebuild too. The cylinder is fine but the rubber seal leaks.

I also have a good one on the 1982 model that is from a 1980.

1980 model:


1983 model:


The 1983 model will fit but may not be any cheaper as second-hand parts from another bike around the same age may come with the same problems.

 

@paulperth - If the seals are the problem with yours, the part number is 45530442315, which superseded the original part 45530442305.

Partzilla has the cheapest price I could find for NOS but if you are only ordering that part from them shipping is more than the part!

CMS have them too.

K & L make an aftermarket one you can find on Amazon or you can try eBay.
I searched on US eBay and found the prices and postage were significantly cheaper, so I bought one

Try searching for 45530-442-315 and see what you find.

Edit: Just noticed your cylinder, lid and diaphragm seem to be missing in the pic. I have the whole lot spare apart from the bolts for the lid. Message me if you want it and we can work out a price.

 

Welcome, Paul. Looks like a great project- good luck with it and enjoy! Regards~

Scott