I bought a used 7 1/2 year old fisher paykel dd603

I have the same model F&P and just experienced similar problems. My top drawer was leaking due to that "not important" thin white tube. It really sounds like you called a general appliance guy and not a trained F&P repairman. The guy who fixed ours mentioned it provides strain relief for the drain tube & wiring loom when the draw is pulled in & out. So no, it is not crucial to the washer operating, however it may be causing all your problems. On mine, when the draw was pushed in, because this tube was broken it was poking straight in to the top drawer and stopping the lid from sealing causing a FLOOD. Also the flood sensor got wet and had started to corrode and was going to fail soon anyway so it really needed replacing. Additionally, my washer had always "groaned/ R-R-R-R-R-R'd" as it wound down the lids on each compartment. The Fisher & Paykel repairman recommended I get the "kit" for it to fix these issues on both drawers. The kit replaces several parts that have been found to cause common failures over the years. He ordered it and has just been back to install it. It cost nearly $300 all up but I reckon is good value. The machine now works like new, and all of the most likely problems that should eventuate have been addressed. It is now whisper quiet when closing/opening the lid too! The downside is that F&P took 2 weeks to arrive first off, then another 3 weeks before the part arrived. :-( If you decide to overhaul your dishdrawer - you won't recognise it! ( btw - I have no affiliation with F&P either, other than my missus loves her F&P DishDrawer and I love keeping her happy! )