Gunk
 

I might be tempted to detach the barrels, and with the butt facing upwards, spray some gun cleaner into the action. Will do no harm, and if it then works, you know it is just gunky. Might still want to have someone competent take it down and clean, but for diagnostic purposes, will do no harm. I have seen old oils harden up like varnish.

Thanks, Greg. Worth a try. I'll hit it with some GunScrubber. Galen Hays

Greg: Good ol' GunScrubber. Good diagnostic step.

Galen: If that makes things work, then have it stripped down and fully cleaned and re-lubed and it will be shooting for another lifetime. Cheers,
Jack