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One more thing you might try: penetrating oil. Douse all the stuck parts in it. Come back every hour or so and do it again. Let it sit overnight. If this works, things will move fairly easy, so the brute force won't be necessary.

If this doesn't do it, then take it to a qualified repairman IMMEDIATELY. If these can be loosened (some brass tuning slides form a bond that really can't be broken) a trained repairman can do it, and it shouldn't cost too awfully much. He'll know whether (and, more importantly, how much) to play a torch on the slides, or to use chemicals you don't have access to. If you can at all afford it, get him to chem-clean the horn and adjust the valves while you're at it. But brute force can cause damage many times more costly than getting it done right.
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Joe Baker, who once twisted a lead-pipe in his younger days.

Personally, I'd take the horn to a repair shop to let them do things right, but if you want to try something...

Try some penetrating oil on the slides, let it work it for a few hours, then warm wtih a hair dryer (don't overdo it). Loop a rag through the slide crook and give a couple of sharp tugs to see if they'll budge. Again, do't overdo it

If that doesn't work, take it to a repair shop.

Lowdown wrote:Thanks Joe. I've got the mouthpiece soaking now. I'll check it in the morning. I'm not sure how I can soak the slides without a big container and a lot of oil.

I knew what you meant Henry. I'll try gentle tapping tomorrow also. Thank you.

We may have one of those 'American English' / 'English English' differences. By "douse", I mean to wet it thoroughly, not to actually immerse it. Of course, it is only the accessible edge where the slides overlap that you can actually oil.

You could wrap a rag around the slide at that point, and keep the rag drenched with the penetrating oil, too.
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Joe Baker, who-za not-a speak-a English-a pretty good.

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Loop cloth through the slide and YANK. Works like a charm and doesn't hurt the instrument.

Biggs wrote:Loop cloth through the slide and YANK. Works like a charm and doesn't hurt the instrument.

This works pretty good for me, too.... but.... I have the tools and know-how to fix anything else that comes loose, breaks, or bends.