The V8s might need timing chains and/or guides at 100K miles. The same is not true on the six cylinder engines since the timing chain doesn't make drastic direction changes. Since your valve cover doesn't come off for valve adjustments, take a rough measurement of chain wear by noting the crank pulley position when the cam is at #1 TDC. There is a more precise method using a dial gauge, but if the rough method says you're within a degree or two of TDC, don't worry about it.

There is a special tool that keeps the chain on the cam sprocket. Dave M. aka gsxr has posts about it frequently. I held the free end of the chain in my hand and had no trouble feeding it through outside of jumping out of my skin the first time the IP gave back the slack. This was on the 300SDL, by the way.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD