I don't have any comments on how my newer (1960s-2000s) instruments -- like y'all seem to have -- are holding up. But my 1924 Buescher Eb tuba is doing just fine. I've finally decided to sleeve a standard American-size receiver onto it so I can use my Kelly 25 mouthpiece (and potentially some others) without the benefit of the Matt Walters adapter I've been using.
Gary Merrill
Wessex EEb Bass tuba (DW 3XL or 2XL)
Mack Brass Compensating Euph (DE N106, Euph J, J9 euph)
Amati Oval Euph (DE 104, Euph J, J6 euph)
1924 Buescher 3-valve Eb tuba (with std US receiver), Kelly 25
Schiller American Heritage 7B clone bass trombone (DE LB K/K10/112/14 Lexan, Brass Ark MV50R)
1947 Olds "Standard" trombone (Olds #3)