I have a 1990 300E with the same problem it is fairly common on a higher mileage M103 Motor. Valves guides and seals are in order. But you can go for quite a while with the ticking your experiencing. I recommend going back to the factory spc. 10W 40
The thinner oil gets into tighter spaces to get everything lubed well, in fact this could be your problem have you recently converted to 20W 50? If you go back you may notice the lifter noise disappear!
1957 Dodge D100
1967 VW Microbus 21 Window
2004 Beach cruiser bicycle
"It cannot be emphasized too strongly or too often that this great nation was founded not by religionists, but by Christians; not on religion, but on the Gospel of Jesus Christ. For that reason alone, people of other faiths have been afforded freedom of worship here." Patrick Henry 1776