Update: I re-soldered the bridge that binds the leadpipe to the bell and eliminated the play and noise of the piston guides by coating them with a thin layer of two-component epoxy resin, now it's perfect. By the way, a new purchase will arrive later this month and it will be a surpraise. I can anticipate that is a Wessex, let's see if anyone guesses.
2007 Besson Prestige 2052, 3D+ K&G mouthpiece; JP373 baritone, 4B modified K&G mouthpiece; Bach 42GO trombone, T4C K&G mouthpiece; 1973 Besson New Standard 3 compensated valves, 3D+ K&G modified mouthpiece; Wessex French C tuba, 3D+ K&G modified mouthpiece.