Replace it with an Amado, Saturn, Pollard, etc.?( http://www.dwerden.com/forum/showthr...lard-water-key) Really easy and relatively inexpensive (especially since you already have the hole in the slide!). I put Amado keys on all the tuning slides of my 1924 tuba. They work fine. The only thing you need to worry about is to lubricate (valve oil) them regularly. Also, it's pretty typical to drill them out with one drill size larger (which I did) so they'll drain a bit faster, but that may not be necessary.
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)