I replaced both front side marker bulbs 99 E430 while I was in Canada. I took the burned out bulb W5W and I went to Canaian Tire to find a replacement. I couldn't find any bulb in W5W. I found a few bulbs that were similar in shapes and size. So I went to MB Canada at Markham, the parts department sold me a couple #168 bulbs. When I showed him the OEM W5W, he said that #168 would fit. I plugged it in and it worked.
After the Canada trip, I went back to Boston Wal-mart and checked out the bulbs. I found the GE W5W $4.50+ and GE 168 $2.00. If I didn't know that those 2 equivalent, I would opt for the expensive W5W.
As far as the owner's manual, it only shows the candle power of various bulbs. It doesn't list the Bulb #. There are too many variation among the manufacturers. When in doubt, always take the burned out bulb and match it at the stores.
99 E430 Sport