Another web site to try is www.nada.com You should be able to get book price there. I would also look at www.autotrader.com to see what others in that range are going for. As far as how long they last is hard to say. I have seen these cars with close to 500,000 miles on them and still going. If it is well taken care of (which is sounds like it is) you should be able to get better than 300,000 mile pretty easy.
Hope this helps....PLEASE ACCEPT
Sorry, The blowby is going to be pretty normal with that many miles. The compression rings get worn over time and allow some compression into the crankcase. I don'tt understand what you want with the est. mph.
I am sorry I don't know how many miles per gallon it should get. I don't want to try to guess either. You may be able to go to mercedes website and get that info. Good luck and God Bless.
P.S. The reason I suggested autotrader.com is so you can check your area of the country for pricing due to cars be worth different amounts in different parts of the country. Hope this helps...Thank You