The plot thickens
Well, what do you make of this?
I checked my 560SEL and, yes, it has shields both sides as you say.
I checked back to the manual where I got the idea it's only on the driver's side.
The reference is in the M117 engine maual, 22-211 (Removal and installation of front engine mount), B - Model 126 where, under para. 5 (Installation) it states: "The shielding plate is located on the left"
What to make of all this?