5k sunroof tilts but won't open much

[Wallace White]

The weather is so nice here in the Bay Area that I'm set on fixing the
sunroof in my 5kcstq. It will tilt back and forth nicely, though it does
make a clanking noise just as it closes. But it will barely open (i.e.
slide back) at all. It moves back far enough to lower the trailing edge
of the lid, but then it jams. 

I've moved the sunroof headliner out of the way but I don't see anything
wrong yet. The slot profile parts are the newer, updated kind. (Build
date is 12/86, before the change, so I'm glad to see this was fixed
prior to my ownership.)

Any tips?

- Wallace
  '87 5kcstq 170k