Don't worry about the grease - Mine looked much the same 2 years ago!
I assume the "catch" drops into the "lock" position if you give it a good push?
I'd start by throwing some degreasant at that spring assy at the top of Pic 3 and the hinges on the catch assy at the bottom of the pic. Once all that congealed mess is dissolved, try it again, then re- lubricate as required.
If you can't get the degreasant to stay in place long enough to do anything useful, 3-in-1 do a foaming degreasant that sticks for about 5-10 mins and dissolves the grease as the bubbles slowly burst. Halfords for about £5 last time I bought some.
Any serial numbers/Age/# Cyls? There will be a microfiche out there that might help me help a bit better......