438,000 miles is very impressive.
At minimum, with similar care and oil changes, we should be able to expect at least this much on an M104.
On another note, two years ago I was at my Mercedes mechanic's shop, and he had a 1992 400E with 44x,xxx miles on it.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".