CAT C13 Acert KCB, Break in period

No its leaking at the valve cover, the bolts for that valve cover tighten into the base but the threads got messed up so I used a heli coil kit and fixed em but it's still not tightening the gasket down enough so I got a leak in the back

 

I'm looking into those gardserts right now, do you know what size I'd need?

 

I started working at the shop where my dad who owned a trucking company got his serviced at, I started when I was 17 and picked up quickly, rebuilt one of our units last January so I'd thought I'd give this one a try, my brother and I own the company now and dad retired, brother handles dispatch and I do maintenance, hopefully everything goes well, I appreciate the praise thank you!

 

Do I gotta somehow remove the old heli-coil? Or re thread it with that in there

 

yeah mine are on exhaust side maybe the heat does somethin to em, okay ill give it a shot, ill take the base off just to be safe ill have to adjust the jake brake again, thank you!