Coolant dumping - freelander 2

Hi, my freelander 2 (2007) has had a slight coolant leak for a while that we couldn’t find!

Until this last week! It’s dumped all coolant, wouldn’t hold, overheating and heaters not working! It went to the garage where they found a coolant pipe at the back had blew as there was a slight fuel line leak dripping onto it weakening it. That has been fixed. When the garage took it on a test drive it blew off the bottom radiator coolant hose, it done this 3 times, replaced that as it was weak and the tank too and that was fine. Now the car is running, heaters working and not overheating! However once we shut the engine off the full coolant system is draining (****ing out) from the back middle offside to the passenger side a little until the system is empty! But then after filling it again it held for 2 10min drives and didn’t drain. When I went out 2hrs later the full system had drained again.

I’m at a total loss. The garage is saying head gasket now but we still have a little hope, we love the car and don’t want to part with it especially since it’s still driving so well!

No head gasket symptoms and oil is fine.

Mine is pressurising the coolant which has been getting steadily worse. I used to need to top up once every few months, driving it normally. However I now need keep mine to under 2000 RPM, and less than about 50% throttle, or it looses the coolant quite quickly. If I use more than about 50% power, then the coolant pressurises enough for it to blow out the tank overflow, which makes the inner wheel arch and wheel well wet with coolant. If I drive carefully it holds its coolant for about 100 miles before the light comes on, so requires topping up.
If I drive at motorway speeds, the coolant needs topping up at 30 mile intervals, but it has been getting steadily worse over the last couple of years.

I believe my issue is HG related, as I used an aftermarket gasket and bolts when I replaced my head, and I subsequently found my torque wrench was under torque by about 30%, which would have effected the clamping load of the HG massively.

I'm going to be doing mine again soon, maybe over the Xmas holiday, but I'm going to be using a genuine HG and bolts this time, and making sure the bolts are torqued up correctly too.