I have and had Rancho shocks on vehicles for over 20 years. The Ranchos adjustable shocks we put on our bought new 2004.5 Chevy diesel truck just 2 months old in 2004 for hauling our heavy TC's are still on there today and still functioning as they should with over 200,000 miles on them. Had them checked late last fall before going to Florida for our annual 2-1/2 winter and visiting family stay.
Rust usually takes its toll on shocks after many years and to help deter rusting I had masked off the shock control areas of the 4 Ranchos and sprayed them with a very good undercoating aerosol can spray and let them sit in the sun for about 2 weeks to bake and dry so they could be handled. Yes, they are all still rust free today so it really works. It is the drying skin over undercoating not the sticky gooey tar stuff that stays sticky.