I would also vote to remove any grease n grime from where ever possible on the action, but gently,then you will get to see whats what,
If you have access to one of those water vibro cleaners, n can take it apart a bit, that might work wonders.
If not,a tooth brush & some soap might work...or some of the above, But work with the gentlest way first.
Put up some before n after pics , so we can see if we were right,,eh?
cheers n good luck
franc