I had my share of issues with 99 300td. The last one was one of the most expensive. Because during warranty I been to the dealer 3 or 4 time regarding steering noise at 54k MBUSA approved the replacement of the entire rack&pinion assembly (parts about $2k + labor about $1k) all covered by MBUSA.
At around 40k the transmission module was replaced because
software glitches made shifting eratic.
There were a number of other little issues. Since I started taking more care myself, knok in wood, things this year went well.
If the warning lamp indicator comes on when you brake it might be the wire harness for the fog lamps. The dealer should replace them free of charge if in warranty.
Good luck, Pat