2011 f150 5.0 156000 miles.
Still runs like new but but has started using a lot of oil (+ - 1qt.-1000) no leaks found, doesn’t seem to smoke. Replaced pcv valve, no change. One mechanic told me to replace the valve stem seals, what’s your opinion.
So we'll assume this "one mechanic" took the time to pull your plugs and inspect them (burning a quart of oil every 1,000 miles will leave evidence on the plug(s) of the offending cylinder(s) ) and then did both a dry and wet compression test and a leak down test on those cylinders to rule out rings or a damaged head gasket and then he "landed on" valve seals.
You aren't complaining about driveability issues or excessive smoke so the only concern right now is the long term health of your catalytic converters burning a quart of oil every 1,000 miles.
They aren't going to like that very much.
Maybe dump some catalytic converter cleaner in the fuel tank from time to time and when she starts to smoke or foul plugs, consider the repair.
I would look at getting into a different vehicle.
That is a LOT of oil to have disappearing. If you aren't burning oil and there are no leaks you can find, all that oil is getting into internal places of the engine where it shouldn't be. You would need to tear down the engine to truly see where the problem lies and to do so would cost a good chunk of money.
