Glad to see you got it open. I suggest spraying with a thick spray lube, like LPS 3 or Krown T40.
The mechanism can be easily sprayed from the exterior. I open the hatch, get it mostly facing skyward, lift the handle with one hand and spray lubricant in the two openings that reveal themselves when the handle is lifted. Spray in the keyhole for good measure also. Then just let it sit for a few minutes with the hatch open.