My experience on my 95 is if you jack with it plan on replacing,the one in the manifold is not that bad to do, the one on the water pump is easiest just to replace the whole pump, just make sure the new fitting is the new style, avail at most napa's hope this helps.
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68? It's all figured out untill you get it apart.
Is it Sunday yet???
68 Project
68 SWB frame off/98 Vortec with stock FI/power everything.
95 ECLB 2500 with 346,000 on the clock(the original HD)
99 Lesabre-wifes ride
08 Crew Cab LTZ-All Mine
89 SWB 5/7 drop-Son's first ride.