Well, I tried a few things, but the lance is stuck. However, I found, in the bottom of an old box in the shed, another lance that fitted!! It's one from an old Waxoyl kit. It's fairly crude and delivers a bigger flow of fluid, so I had to be careful. But I have done both sills and I think I've found all the layers hidden in there.
As the tube is still stuck. I've ordered a small cheap borescope to stick on my phone, just to see if I can see what's jammed it. But that's more out of interest than need. My old borescope is too big to go in through and hole.
But that's it until tomorrow. The Aerosol has emptied itself, so another has been ordered, along with a couple of spare lances!!
One issue. I levered out a plastic insert in the sill that holds the plastic cover on the sill. The metal is very thin!! It bent easily and I had to hammer it back...