I noticed my rear passenger tire was low on air about a month ago. I filled it up and it was okay for 4 weeks or so. Today, cool day, tire is low again - doesn't even register on the pressure gauge.

I don't see a nail or anything that looks like it may have punctured the tread. I have a little curb rash.

Questions are:

1) best thing to do - take wheel/tire for dunking test to see where leak may be?

2) if the tire needs to be repaired, can it be done so the S can be driven at high speeds on repaired tire?

MY 04, approx. 11M miles.

thanks for your help.