Yes, Richard Burton died before filming this (he's only seen in the pre-title sequence that is footage from the first Wild Geese film---and really of no consequence to the sequel's story). Perhaps Burton saw the script for this mess and realized there was no reason to go on living. There is certainly no reason to go on watching this thing, that's for sure. It's all about some muddled kidnapping of Rudolf Hess from Spandau prison. Seems the British, the Germans, the Soviets and the scriptwriter all want to have a hand in either killing or keeping Hess alive. When we finally get a look at Hess, after 90+ minutes of tedious intrigue, it turns out that that the kidnappers have goofed and grabbed Sir Laurence Olivier instead---and not the good Olivier, but the decrepit 'Jazz Singer' version. Sir Larry, that sly ol' dog, thinks he can fool us with a Hess-like unibrow and that 'Marathon Man' German accent, but we're not buying it. The kidnappers aren't either and dump Sir Larry/Hess at the French Embassy in Berlin. The real Hess died in 1987 (hung himself in his cell, perhaps after viewing this film) and Olivier followed in 1989. Time passages.....
(I personally liked this one better than the first)