Wow...theSenior is among the oldest W-C toilets...introduced sometimes before 1935. The oldest catalog any of my contacts at Thetford who were with W-C before Thetford bought them can find are only two--one from 1901 in which there are no toilets and one from 1935 that includes the Senior. We know that there was a Winner sometime between 1901 and 1935--which was most likely to have been the very first manual piston-cylinder pump toilet, but it had apparently been discontinued before 1935 because it's not shown in that year's catalog, which includes the Junior, Senior, Regular, Monarch,
Crown (not to be confused with the Raritan Crown Head, which was one of the first macerating electric toilets) and the Imperial.
So if your W-C Senior is still in good working condition, you have a real collector's item! Unfortunately there isn't much demand these days for bronze "thrones" made to last 100 years...and no repair parts either any more either 'cuz there's no profit in repair parts for 'em. The Groco Model K is the only one still in production in the US. The only other one still made anywhere is the "Baby Blake" made by Blakes in the UK...the same company who makes the Lavac.
If you'd take some photos of it from several angles that show the pump in detail, I'd love to have them!