I am not exactly sure what bolts you are referring to. The bracket that holds the pump and reservoir on my 92 400 is held by three bolts, two 13mm threaded in from the rear of the bracket (sounds like the ones you have found) and one more allen head bolt (can't remember the allen key size, sorry) that comes in from the front, just above and to the right of the belt tensioner adjustment nut. There is a recess in the bracket, so the bolt head is hidden.

One of the bolts from the rear required a 3ft extension on a socket which you had to come in from behind the engine mount. It is hard to see.

I left both those rear bolts in place until you replace the bracket--the top one is hard to get your hand to.

Hope this helps!

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Peter
1985 300TD 4-speed 212K
1992 400E 343K
2001 E320 72K