Magnepan Mylar Repair

One of my MMGs has started doing the bass slap and I think the issue is the mylar has stretched.  I took off the sock and visually nothing looks wrong. Does anybody know how to re-tighten the mylar?  I contacted Magnepan and they are only doing warranty repairs for the foreseeable future. 
Very carefully with a hair dryer set on the lowest setting and moved around quickly.  Don't hold on the same spot for very long.

I've used this method on Maggies, Acoustats, Martin-Logan and Sound Lab speakers with excellent results.
@mofimadness Thanks for the info!  Use the hair dryer on the whole mylar or just the area that's slapping? And overall, how long should I run the hair dryer?  
Never done it myself but there's lots of good info on other forums (audio asylum and audiocircle) and Google.
Good luck
A lot of info on this subject can be found on the Planar Speaker Asylum site. Magnepan is by far the most-covered planar brand there.