The Wilcox-Crittenden Winner dates from the 1940s...maybe even the '30s. Not only do the degradable rubber, leather, cork etc
parts in kits wear out over time, but so do the machined
bronze parts. So while I'm certain that the toilet can definitely profit from a
rebuild kit, I'm not sure that a
rebuild kit will solve your specific problem.
However, there is one person who WILL know what you need and whether you can still get it: Jock Allpress. Thetford bought Wilcox Crittenden several years ago (and promptly discontinued the whole W-C product line)...they got "JockO" who'd been with W-C for at least a couple of decades in the bargain.
Email him at
jallpress@thetford.com