Ahhh sorry I didnt read your post thoroughly. Im coming from Honda/Yamaha so im quite surprised (after doing some research) at how often these “390 RC/Dukes” need valve adjustments at such a short interval.
It seems the labor($$$) to perform the check is quite different from the actual adjustment. Performing the valve clearance CHECK requires the removal of the valve cover, rotating the crank, and sticking in the feeler gauges to see what the clearance is.
Performing the adjustment requires the valve clearance check, removing the camshafts, and reinstalling the correct shims which requires a whole lot more labor.
Keeping those two facts in mind, it’s in the dealer’s best interest to charge you for a valve adjustment whether or not you need it. I suggest you check the valve clearance yourself (and bring it to the dealer to perform the valve adjustment) or HOPE the dealer/service writer/technician remains transparent enough to charge you for what your bike really needs. It’s a tough pill to swallow, but fixed ops (the shop) are what keeps a dealer open; not the sales department.
I know this wasn’t exactly the answer you’re looking for, but someone who is mechanically inclined may find this information useful.