end of warranty suggestions

I am nearing the end of my 50k miles warranty for both my 1997 S320 and 1998 E320. All have been maintained through the dealer and my self with q5k Mobil 1 oil changes, all other fluids changed q 2 years, along with the regularly scheduled maintenance. Except for a recent Oxygen sensor problem with the S320, everything has been terrific. So are there any recommendations in terms of testing or other preventative maintenance that I should do before the 50K has run out? ie I've read about a dye for detecting small oil leaks, good idea or not?

Thanks in advance for your ideas and/or suggestions.

Lionel