You guys still building your own proportioners? I built one about 4 years ago I guess and I just take it apart every year and re-do the fitting paste, etc. Thinking on making another one due to all of the SH run through the PVC, probably getting brittle about now. Some parts Check valves are the same ones others' recommended here a few years back. They hold up extremely well. Can't believe how those little Hastelloy springs hold up. Especially the one I use on the Mini-Prop I made for DS'ing. It never gets rinsed. And the spring holds up all season long,.. Check valve only gets replaced the first of every season.
I remember someone showing an "off-brand" proportioner someone was making and selling for fairly cheap,..Wasn't sure if they're still available or not.
I have three I have made over the years. I don't do anything until something isn't working. I did make it so we can easily rinse the valves and check valves.
I'm not sure who is making them except Mid West. I got one from him and replaced the soap valve. It was too small.