I wouldn't wait 13k-15kes to change the oil if you want to keep the car. Also if you are going by FSS you better make sure to run Mobil 1 0w40 or something from Amsoil.
Over at MBworld they said it best:
Follow FSS on the leaser, for the keeper change every 5k+/- miles.
Also the trans is according to MB filled for life. Their is a lot of info on this site about them. You have to use the MB trans fluid. You need to buy the dipstick tool, and you also need some way to measure the fluid temp You have to check the fluid level at a specific temp, proper fluid level is critical for shifting.
My friend had his E300D done at the dealer for like $200, it shifted better with the fresh fluid.
Don't be in such a rush to rebuild it, think $3k-$5k for a rebuild.