Date registered: Jan 2013
Vehicle: 90 350SDL, 98 S420, 97 SL500, 94 S420, past owner of W108/W112/W114/W123/W124/W126/W140 & W220 cars
Location: Tampa, FL
Mentioned: 8 Post(s)
Quoted: 604 Post(s)
Not to belabor the point, but another example that I have first hand experience with is the seal on the W123 chassis. If you have an OEM seal and inspect it carefully, you will find that there is an additional lip in the lower corners that helps to seal this critical area. It's almost impossible to see unless you invert the seal in this area and look closely.
Aftermarket seals do not have this lip. It's due to either an oversight when they copied the OEM seal or an omission to cut costs in manufacturing.
Fortunately, I had a very, very good aftermarket parts supplier who knew a lot of these differences, and shared his knowledge with his customers.