[Bridwell]

One thing to consider is the type of front of the card. A Topps card or a T206 has a glossy coating on the front that is able to be cleaned. I've tried Un-Du or Quickie Gunk & Goo remover. Sometimes even water will do it. Other types of cards you would damage with that approach because the paper is softer. That's why it doesn't work well on the backs of cards. You could also consider heating the front with a hair dryer. The heat can loosen up the adhesive so you can wipe it off. If that didn't work you could try the soaking technique.