Cheers, I'd pretty much come to that conclusion. I think I'll try and stick the old one back in and see how it goes. New handles are £24 so it's worth a try first.
BTW, the button that releases the handle from the wand had a lot of gunk underneath it, so maybe it wasn't fully retracting when pressed down. Cleaned all that out and now I can press it down further. I guess this may have been the original issue but it resulted in a lot of pulling and wiggling in frustration, and maybe that is what actually caused the seal to distort.