S5 4.2 V8 Coolant Leak

[LeedsS5UK]

Good evening all, I recently purchased a 153k mile 2009 S5 4.2 V8 with pretty much full history, had a new timing chain 2 years ago, freshly serviced this year. The person who owned it before me had it 2 years and didn’t use the car much, mainly at weekends. I am now using the car daily. 
Car was working fine for 3 weeks then a few Sundays ago it blew the coolant expansion tank lid off as I was parking it up. Since then it has been into a local garage who diagnosed a air lock and bled system and then it developed a small coolant leak (seemed to be coming from the front driver side area underneath), this was diagnosed as a crack in the expansion tank and that was replaced yesterday. However the car is still leaking coolant. This only happened when the car had been used for quite awhile and gets hot then I park it, turn the engine off and come back 30 mins later to a small puddle of coolant (about 3/4 litre). 
I have checked the oil cap for creaminess, smelt the coolant for exhaust gases and there is nothing. Car runs spot on and doesn’t over heat. 
I believe there must either be a hose with a dodgy connection on or I am told these also suffered from a dodgy cross over hose that goes round the back of the engine that feeds back into the coolant tank.

Any help would be most appreciated