I've owned my 4003 for around 9 years and someone else owned it for around 7 years before I bought it. I never made any adjustments as it was setup pretty well and in the 4 years I was gigging with it nothing much changed. However, since moving to the US around 5 years ago, the bass has seen much less action and has sat on the stand (alongside my 360) going through seasonal heat and humidity changes.
I first noticed that the bow on the 360 had increased and made the necessary adjustments to get it feeling right again. The 4003 had a similar increase in bow and when I popped the cover I found that the 2 truss rods looked very uneven (see pics). There doesn't seem to be any perceptible neck twist despite the many years in this state but that doesn't make it right.
In researching I've read that some folk just use the single rod for adjustment and tighten the other just enough to stop the rattle? The guy I bought the bass from had a tech who did his setup and I'm wondering if this is his doing?
I put 1/4 turn into each rod and that has brought things back to an "acceptable" bow but the uneven setup still makes me uneasy.
Any useful comment?

