Is it heating up? Rust is not uncommon in a 23yo vehicle, at all. It needs a thorough flush with a cleaning agent (prestone flush) and a refill. I really don't trust "mechanics" with these trucks. I had rust and sludge in my 90, replaced water pump flush and fill, its fine, antifreeze is still clean. I would be more concerned with the integrity of the mechanic.
"I like fun" Edd
Clawed: 90GW, TFI, Streetfire, 3"lift all spring, 31"BFG ATs, working RKE, Edel2131, Holly 1850, mild cam,
05 Renegade OME 927, 947, top plate, JBA 4.5s
"Just Jeepin it real"