You probably have already tried but;
check for coolant in thr radiator, coolant in the oil, leave the radiator cap off and crank it over checking for air bubbles, check the tail pipe for coolant signs, double check for possible bad fuel filters,pull the injectors and check for any coolant drops and do another comp. test. Do all the easy things first and try not to panic, I,ve been there a hundred times.
Find out any history from where it came from.

Best of Luck

__________________
Ricali

03 C240 4matic wagon
95 300E 234,000
7 prior 240;s 5 still going
81 300sd gone
65 230sl gone
49 Studebaker Champion
90BMW convert.167,000
60 Dodge D-100