Are you using any thing to soften it?
Trinity sells a product, Sticky Fingers, which is normally used to soften tires. It should help.
People use a router to clean old glue off all the time. You use the same bit you use to cut the recess.
On a flat track, it's fairly easy to a good job.
On a banked track where the track isn't flat, you need a small router base and someone who really knows what he is doing.
I've seen tracks butchered by guys who supposedly did know what they were doing and obviously didn't.
I personally thinks it's better to gut it out removing it without a router. At least you'll save the time of repainting the recess.
You definitely don't want to glue to bare MDF.
Mike Swiss
Inventor of the Low CG guide flag 4/20/18
IRRA® Components Committee Chairman
Five-time USRA National Champion (two G7, one G27, two G7 Senior)
Two-time G7 World Champion (1988, 1990), eight G7 main appearances
Eight-time G7 King track single lap world record holder
17B West Ogden Ave., Westmont, IL 60559, (708) 203-8003, mikeswiss86@hotmail.com (also my PayPal address)
Note: Send all USPS packages and mail to: 692 Citadel Drive, Westmont, Illinois 60559