Thank you all for you great advice and insights. Here's some responses based on your inputs.
I was hoping to do this without lawyering up but may have to
. I was hoping there was a legal precedent regarding this I could leverage.
I'm very certain my neighbor will not give up any lakefront with a LLA as he wont even afford me 6-8' I've asked for by moving the dock - which would be hardly noticeable for him but would do wonders for me as I'm giving up 10' on the other side of my 75' of shorefront for my dock to my other abutter.
I'm certain the dock is legal - my home has been in my family since 1969 and I recently purchased it in 2018. I do remember him telling me it was re-built and he changed the sections from 8' to 10' (post 1978 - start of seasonal dock regs) but I have nothing to prove it.
I did call DES docks division - they said the dock is existing and as long as he didn't change the dimensions or location there's nothing they can do.
I did get him to move the ramp over 1-2' (but now the other end of the dock is closer - actually right on the line - I have a picture of a string line to prove it too!) Perhaps considered a relocation?!
. I checked DES onestop and don't seen any permits issued to him.
The town hall records is a good suggestion and worth looking into.
The dude tries to make alot of his problems mine, I could tell you some stories...but I digress. The claim about water level in November is real and valid. He would have to float the dock to his launch point about 6-8' due to a tree being in the way where it would sit in the water if he was to move it over. But the water is so low in November the first section is practically out of the water. I think there's ways to do it, i.e. push the dock out further to where it will float (he uses a tractor to launch and pull it out), float it into place and then yank it out. I'm sure there are other ways, but like you said his problems should not be mine.
I did think of the same idea about suggesting moving it back to the launch point after labor day when the water level is still high enough. I have not approached him on that idea yet but I have a feeling what the outcome will be.
Again, thanks for all your feedback, more ideas welcome.