I had the same issue with a newish 600t that started dripping out the back and spitting air every so often one day after 6 months use, reseating everything would eventually stop it until it was disturbed again, no idea what was happening read this thread then realised I had used the inlet/outlet connector from an older 350 that had sat around for a yr, before I used it, bought a new one for £15 and fingers crossed OK, suspect the 2 tiny seals had dried out, I now spray the rubbers with silicone spray, thank you everyone this thread was really useful,