Before you do anything else (IMO), if the 2 wiring harnesses are original - change them both out. They may look fine from any exposed areas but under all the wrap I'm willing to bet money that the insulation is cracked or gone in places and the bare wires are in contact with each other causing the gremlins. BTDT on my car years ago. The orginal harnesses were made out of a bio-degradable castor bean concoction and MB has admitted that they 'degraded' way too fast causing all sorts of electrical problems. Original owners of such sub-standard quality were 'goodwilled' new harnesses (usually) up until very recently.
It is possible that the ETA is fried on these very hot running M119s but first and foremost, rule out them wiring harnesses. Just my 2 cents living with this car for almost 10 years now.
