jari, sorry to hear of your dilema.
if you really like the car, the previous advice to set it straight and look forward to many miles is good.
as our ever popular SPOCK says: live long and drive a MB!
if not, a couple of thoughts as to recourse:
#1 carfax is basically a complilation of public DMV records. they do offer a guarantee, but only that the info they pull is correctly reported from the those records.
#2 the 1st mech: it sounds as if he made have performed a less than through inspection, but unless he was an actual party to the purchase agreement, i think he is out of the loop. however, he would be liable for charges if he billed you for work that was not performed.
#3 the PO: when he signed the title, he either checked "actual" milage or not. if he received the car under an "actual" title, and didnt change the motor or speedo, he did not perger offical documents. he may have lied about being orig owner, but was not in that case, the one who "cooked the books". dishonest at least, possibly criminal.
MB dealer (or possibly one of the techs here who have friends in high places) can pull the "master" file for the cars VIN, and that along with any previous title info may give you the opportunity to reach the origional owner (and any intermediate owners) to determine the cars "real" history.
good luck either way. - benton