My suggestion is still this: Allow gunner to get on an overheated gun using stamina, and remove the increased gun arcs. Change heatsink to reduce fires at X per second, so it does not get rid of fires right away, but would over time. With the new reload mechanic, pop stamina, get on a hot gun, hit heatsink, and leave. The rest takes care of itself.
I also suggested a tool a while back called the 'Impact Wrench' (or babysitter). It rebuilt and repaired faster than a pipe wrench, but had a cycle shorter than the spanner. In effect, you could only repair one thing very fast because you could not leave it. Unlike the pipe wrench, you could not give things a hit and run off for 5 seconds.