Cummins ISX overheating and coolant issues??....

hey guys,
i have an '08 prostar with a cummins isx, im a die hard CAT man but this is our only unit with a cummins the rest are c13's and c15, it runs good on power but lately for the past two months its been heating up while idles, it gets to around 210 to 215 in around 20 mins however when its driving on the road its fine, the drivers had brought it back before this with engine overheat code twice as well as a coolant low code, it had an egr cooler leak, not internally but it was cracked on the outside brackets, we got it welded and we've checked inside numerous times after but there is no coolant, the truck does loose a little coolant occasionally, the doc and dpf have been cleaned, it was running freeflow bcs i took the thermostat so it wouldnt overheat even more but its winter now and the drivers need heat so i put it back in, recently i noticed on an exhaust leak around the outlet to the stack there is a white stain almost like sprayed out of it, as well a dripping sort of stain coming from the top of the stack, the fan works fine as well as the water pump, there are no bubbles in the reservoir to indicate head completely and the truck has fine power also no smoke from the stack as far i can see when it drives, we're planning on taking the exhaust manifold to take a look inside the cylinders for any coolant, i apologize for the lot of readin but im trying to give u guys everything it does, what do u think im lookin at here? head cracked, head gasket, sunk liner? anything else ? lemme know thanks guys

 

thx and yeah i get ya, i put a new thermostat in, and yes after it drives for a while u can see that coolant has come out of the cap and its under max so im not overfilling it, and we set the fan to kick on at 195 just to be safe