Suspected head gasket failure? Coolant leaking with no visible leak, water in exhaust, struggles to start

Hi,

For some while now (at least 7-8 months) I have had a coolant leak. I cannot find where it is leaking from, there are no tell tale splash signs anywhere/crusted deposits etc. I have to replace the coolant at least every week (depending on milage). Obviously this would be expensive so I have just been using water.

My exhaust gurgles like there is water inside and leaks from the front join of the muffler box nearest the engine. The drips come out maybe every 5 seconds, so there is presumably a fair amount of moisture in there. There is also a leak apparently from the rear right hand side of the engine, near the firewall, as I can see water dripping underneath the car, although it seems to be coming from further back than the firewall. (I have checked and cleaned the drain holes in the battery tray and this leak is still there). I cannot see any leaking from the expansion tank and all the hoses and respective joins seem fine.

The engine struggles to start sometimes (needs about 5-10 seconds of turning over with my foot on the gas/ pumping the gas pedal) and for a little while after starting if I don't keep the gas down, it sometimes just turns off (I thought this was a problem with the choke maybe?). Once running it seems to run fine (very occasionally can get a bit lumpy or there is a loss of power for a fraction of a second) and although the coolant runs out and the warning light beeps at me alot, the engine doesn't overheat, sits at 90 degrees like it should. The oil temperature never really climbs about 60. I have never had to call out a recovery truck, it always starts, even if it takes a while.

Lastly, there is sometime quite a lot of condensation in the car (as in it froze on the inside one night and I had to scrape it, and when not frozen, there are drips like you'd expect after rain on the outside, except on the inside). Occasionally when the de-mister comes on, it mists up the window more, and then proceeds to clear it like normal.

Does anyone have any idea what may be causing this all! From what I've read it seems most likely to be either the head gasket or an engine block fracture. Any help would be much appreciated! Sam

Oh and the model is a 1999 Audi A6 avant 2.4l petrol V6 30V