You do realize this thread is 5 yrs. old? But since you fired it up again, I have never left anything in my lines but water. Had my graco for 10 yrs with no issues. Just saying. They have stainless steel parts and are an airless design hence minimal rusting.I maintain alot of pumps at my 7-330 job outside of side painting. Mineral spirits will make the pump last longer if you're storing it, alcohol or other thinners would evaporate and dry out the packing, which could cause them to crack or rip when you start it up after a long time. List gotta make sure the latex is all flushed out like mentioned above. The key is the oil layer on everything. If you had to you can also use a light oil. If you want a more friendly idea, could try out a cooking oil in water, so it would leave a film. Just make sure flush the equipment with the appropriate fluid before spraying to get any residue out.
If your using your pump for mostly latex, I certainly would NOT be storing with Thinners., unless for long term storage.. If it's a dedicated oil rig then that's different. Just too messy of a switch over.Just to keep the thread going... I tried to resurect my Magnum LTS 17 today and it was stored for 5 or 6 years with just a water rinse through. I had to unclog the reversable nozzle after the pump started pushing through water (I think a piece of dried paint clogged it) but it seems to be working fine now. While I do have the Pump Amor bottle, it is really expensive here in Aussie, and will try Mineral Turps (I think you refer to it as Mineral Spirits) next time. Also getting the pump working without the nozzle first might be a better plan.