If the gunk on the bottom of the iron is really bad, I have used double or tripple ott steel wool and lighter fluid if the stuff is sticky. Of course you can only do this on a steel plate iron. I will barely warm up the iron and lighter fluid will take off the sticky, don't press too had as to keep from scratching the plate with the steel wool. That is why I use a FINE steel wool. Try just a small place to start with. Has worked for me in the past.