mosfet failure
 

How would one know if they had a mosfet fail?

Quite often they go short circuit from drain to source.
Check it with a multimeter on the ohms setting.

I have seen a gate to source short as well but only once.

thank you

I measure 17K ohms across the d-s for a disconnected never used 2sk3563, the same as my used ones, when disconnected. Does that seem right?

Google for it. There are a few simple techniques to test the gates.

can one fail drain to gate?