From what I've heard radial tires should never be plugged but should be taken
off, dismounted and hot patched from the inside, to help preserve the
integrity of the belts. Also, since side walls are thinner than tread areas
they shouldn't be patched at all. These are things that I've heard from
various sources but they make sense to me.
Also, something unrelated: Brake fluid should be replaced every 2 years as it
absorbs moisture which lowers the boiling temp of the liquid and can lead to
brake failure during periods of extended braking (Mountain driving). The
problem is the water turns to vapor which is a compressible gas so the pedal
goes to the floor instead of transmitting the foot force thru the
incompressible brake fluid to the brakes. Also, the water settles in the
lowest spots (wheel cylinders), causing rust and pitting and they start
leaking.
Sorry about rambling on, hope this helps someone.

Tom Smith
Charlotte, NC
83.5 Westie