In one case where a member was having this problem of short PTO switch life, he found the wiring that serves the PTO clutch was chafed by rubbing the pulley till the copper was exposed. I recommended he repair the damaged wiring and check/adjust the air gap of the clutch.
I'm not sure whether (actually don't remember) the additional amp draw from the rubbing wires was over-burdenening the PTO switch and whether his repair to the wires has improved the life of the PTO switches. Maybe he will see this post with picture and respond.

It certainly stands to reason that if his Cub RZT suffered the wiring to rub the pulley and create that problem, other owners could expect the same thing.
It would not hurt to get under there with a good light and give your clutch wires a thorough inspection.
It would also do no harm to run some electrical tests on your clutch to see if IT is drawing too much current.
E-mail me if you would like a copy of the Warner PTO clutch manual in PDF format.

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Mine burned out a couple switches. The clutch showed only 1.5 ohms resistance across the leads. New clutch showed 3.5 ohms. The new clutch fixed the problem.