I’ve had a few shimano chronarch mgl’s and I have found one pretty annoying problem with them. Every time I fight a larger size fish the spool tension loosens up completely. So obviously my next cast results in a pretty bad backlash. Does anyone have this same problem with shimanos without clicking tension knobs? I have a shimano Antares(that has a clicking tension knob) and this never happens. 

I doubt if the spool tension loosening is a quirk of the reel's design as spool tension and drag work independently of each other. Even when the spool is turning as the drag is doing its job, if the spool tension were to become a factor, the spool would still be turning in a clockwise direction as line is fed out.

What I suspect is that the close proximity of the cast control knob, star drag and the swept cranking handle is allowing something to turn the cast control knob during the fight. Most likely, your fingers are brushing against it as you grip tightens. A cast control that clicks to let you know how much you've adjusted it is, IMO, a useless feature that doesn't inhibit the knob from loosening any more than one that doesn't have it.

Never had that problem with my MGL. There is a pressure tension spring under that cast control cap...is it there?

Never had an issue with any of my shimano cast control knobs becoming loose. Or any reel for that fact.

There's usually a rubber O ring on the threads that hold it in place.

 

If all else fails you can put some teflon tape on the threads then put the cap back.

Put a little blue loctite on the threads, and let it completely dry before screwing the cap back on.