I have not had to replace anything on my 2003 Lance that was Lance specific (if that is what your question really is). I did a hot water ignition board, and recently replaced the diaphram of the water pump. The Fantastic Fan lid broke and they replaced that for free (love that company!). That was all commodity RV gear and readily attainable. None of it was a Lance-only item.
I do understand where you are coming from. With automobile manufacturers, they will discontinue parts after a few years and it can really be a PITA to deal with simple problems of proprietary parts. I get your thinking about the slide (which I don't have). There could be wear items there which are Lance specific which you might want to grab a spare of.
HTH,
-Eric
