Yep, that is the tradeoff. The plastic back then, and maybe even today, wasn't UV tolerant so it becomes hard as the plasticizer evaporates.
Actually the best place for buying these trucks is up in Dane/Grumpin's area, the Pacific Northwest. They don't use salt on the roads but also don't seem to have the intense sun of the SW.
Gary, AKA "Gary fellow":
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Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI