This is not a situation I think I could tolerate, but if you're concerned about water collection in it, installing an Amado water key on it is a piece of cake. I put three of these on my old 1924 tuba. You can get the Amado keys themselves from Votaw tool (either brass or silver plated. Then (if you want to do it yourself) it's just drill the hole, sand finish away at the joint, and solder it on. Or have a repair tech do it.
The only think you need to beware of with Amado keys is to keep them lubricated about at about the same frequency you lubricate your valves. You can also disassemble them for cleaning, but that is almost never necessary if you lube them frequently.
I confess that I, too, am puzzled by the problem of fixing the slide correctly and soldering it in place -- unless you just didn't want to wait a week or so for a part that was needed.
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)