WD40 and elbow grease
as for the lock had the same thing on a cavalier i had (sad but cheap) there was a clip on the inside of the door
that had fallen of
just had a look in the Haynes manual think there i a retaining clip inside the door have to take the door panel of to get to the door lock
there is a connecting rod and spring
then there is a coupling and spring clip
if there are damaged this might be the problem?

