https://forum.ih8mud.com/threads/new-seiken-44610-60792-brake-booster.1213795/
$375 at 80 Series, NEW OEM Seiken Brake Booster and OEM Gaskets (2), 44610-60792 - https://www.cruiseryard.com/80-series-new-oem-seiken-brake-booster-and-oem-gasket/
You can go down the whole Toyota vs Seiken vs...
Not a fan of dying, myself.
Polymers degrade continuously from the moment they're made. The molecular chains literally break. If it gets really bad, you might be able to see damage, like the "dry rot" cracking of an old tire. It's exacerbated by things like UV, heat, and ozone exposure, but...
Uh. I just said:
*You* only adjust the LSPV if you've installed a lift. Not "the LSPV adjusts itself". If it adjusted itself then nobody would be talking about adjusting it.