Adam, I don't read that you specifically cleaned the threads in the bolt hole and bolts themselves.
It is common for material built up in this area to make your fastener torquing process inaccurate and clamping force on the joint inadequate.
If this cleaning is in order I would remove the bolts one at a time after draining the coolant and then re-tighten the assembly using an anti-sieze lubricant on the threads and under the bolt head.When using the anti-sieze use the lower figure for the bolt tightening specification because of the superior lubrication.
