When I bought my pop the seller showed me in the boot and then said you have to really slam it to make sure it shuts. He was a retired car salesman so I should have known really.
Today I took a look at it and it seems the lock bolt doesn't catch on the plate that's fixed to the boot opening and it only stayed shut as it was jammed in tight against the recess of the opening. I had to drill out the bolts holding the plate ( can't think if the name of it ) and tried it against the bolt. It seems it's at the wrong angle to catch properly, anyone had similar trouble?