I hope it's not the Headgasket again!!

The truck is a TD5 Auto with 211,000km on the clock. I had the headgasket done at 185,000km due to overheating cause the stupid dealer didn't notice the leaking radiator. At 207,000km I noticed a slight drop in water (been paranoid ever since the h/g went). Turned out to be the radiator leaking again so in goes a new one (R6,000). She has run perfect since then, not a drop of water and two trips to the Kruger Park and Waterberg over xmas. At no point were there any signs of overheating. She's booked in to have the injector harness replaced cause of a slight misfire and now I've noticed a gurgling sound of water running through the heater matrix (as if there is air in the system) when I pull away. I've checked the water levels and she seems fine. will continue to check. Any ideas what it good be? I'm thinking the bloody H/G has gone again and if it has then I'm afraid she'll have to go. The wife is not a happy bunny with all the money I'm spending it.