Ok the issues with G60 Rads or VR6 variants are that the plastic housing has to be on top to make room for the FMIC pipes.
The design is simple the plastic flange is bolted down by two bolts, but the actual threaded housing is built into the RAD itself. A skool boy error is to have over (done this one too myself) is to over tighten the bolts which means the threaded metal sleeve breaks away from the fixed plastic Rad. so eventually the dam thing leaks as you cannot get a decent enough tightness on that flange becuase it spins!
The only way I managed to boogle one is to drill out the metal sleeve and put a new one in using liquid metal as a bond between the new thread and plastic Rad, failing that its proberly means a new RAD but we know how hard it is to get a decent one.
You find that air gets sucked in aswell causing air pockets and eventually over heating been there got that T shirt!
the only thing different between the two bolts is its length but I reckon some dell boy tried sticking a bigger bolt in becuase it was spinning

That flange looks like a Rallye water one same as mine one bolt longer than the other?
What part number is on it?