Thanks for the follow-up answer.
Damn, I have replaced quite a few oxygen sensors on mid '80s Mercedes 4's and 6's engine cars and never had to use such a tool. I have to admit I hadn't even heard of it. Ha,ha,ha! Ah well, you never stop learning. Such a tool makes a lot of sense in case of the 400E. No space in there.
Thank you very much again, your advice has been very educational and helpful. I'll let you know how things went.
Sincerely,
F.J.

__________________
F.J.
81 300 SD grey/palomino 168K miles
84 190E 2.3 black/grey 64K miles (wrecked)
85 190E 2.3 maroon/palomino 92K miles
88 300E desert red/palomino 204k miles
(made to look like a '94-95)
92 400E desert taupe/creme beige 120K miles
(converted to 94-95 E420 looks)