You may have read this but here's another 99 E300 thread with some info about removing the intake manifold bolts plus some pics of the fuel system.

http://www.peachparts.com/shopforum/showthread.php?t=189097

This diagram is useful and has all the o-ring locations:

http://detali.ru/cat/oem_mb2.asp?TP=1&F=210025&M=606%2E962&GA=722%2E608&CT=M&cat=19T&SID=07&SGR=120&SGN=04