[lkchris]

First time you drain the sump you'll get oil all over the threads of the plug and unless you go to extraordinary effort to clean this off, you'll have threads nicely protected from corrosion.

The torque figure for tightening the plug is what's required to crush the crush washer--you're not stretching the plug--and that washer then serves as a one-time-use lock washer. Point being, oil on the threads doesn't hurt.

The threads in the pan can deal with the minimal force that's applied to them, as most of the force is absorbed by the crushing of the crush washer.

Don't reuse crush washers ... which ought to be obvious. Don't omit the crush washer either.