Hatchback doorlock, opens sometimes, not other times.

Good job. I recommend WD-49 for a penetrant (broken bolts, etc.) and for corrosion resistance, but I don't like it for a lubricant because it dries to a waxy coating which is not good for locks or drill sets, etc. I like a penetrating lubricant instead in the locks like TriFlo or Liquid Wrench for locks or mechanisms.