By far your best bet is to hop on in to ye locale repaire shoppe. The service techie there will smile knowingly and take your horn in the back where he'll run a slightly overside sizeing ball down the male ends of the slide and very
slightly expand it so that it moves smoothly but snugly.
There is another method that I was told about that I've used but I promised not to repeat it to anyone who isn't an engineer!
(it requires heavy powertools and hydraulics).
Best go the repairshop routine.