When we last visited the problem, it was Shibby v104 with a different modem at a different place in the same city: /forum/t-603852/n66u-shibby-v104:stuck-at-renewing-wan-dhcp (can't link as a newb) - this was never resolved, I just used different firmware. Somewhere down the line (I'm guessing by v128) DHCP started working again.
Here is the new info.
Started on v130 (no problems for months).
Upgraded to v135 (being careful to erase NVRAM). VPN and AIO have the same problem.
Back in business with v132.
What's the regression?