Stuck T1 slide

Howdy!

I am trying to restore a horn to playing condition. It has a stuck first valve slide, Bb side. I have been hitting it with heat and WD-40 daily for about a week with no progress. I'm wondering if folks can give me other advise on getting this sucker loose. I pull by running a polishing cloth through the crook and jiggling, pulling hard as I can.

The horn does not have enough value left to consider sending it off for repair; I need a DIY at-home solution.

Thanks!
- Pete