Quite understandable. I'll take 'easy and inexpensive to fix' over 'it's a work of art- when it works' any day, especially with something like a toilet.
I'll also note that fluidmaster hasn't really changed the design of their fill valve in quite some time. I was able to replace the top half of one whilst keeping the bottom half screwed into the tank. That at least got the thing to stop running for a couple weeks until I got the funds to replace the entire toilet. (which was a 1st gen low-flow kohler made in '96)
My next plumbing adventure with my house is going to be having the last bit of galvanized supply lines replaced; seems the plumbers that I hired to re-plumb the house when I bought it completely ignored the master bathroom. (I'm using a different plumbing company, obviously- fool me once and all that...)