Possible sabotage? Additive added to car needed full tank of gas he said..help?

Car had had oil change a 1000 miles ago and was not scheduled for change for anothr2 thousand we have routine maintenance done 1998 ford escort LX 271,000 Ford did a 75 dollar full diagnostics check and told us it needed a tune up...sears was cheaper...we went and got it done...sears said they added some type of additive [[Ford found no problems before with engine just needed tune up and brake work front brakes brand new now]] car had a new weird vibartion to it after sears did tune up....they said they added some type of additive didn't say much else other then get a full tank of gas in it to help. Car broke down after driving less then a quarter of a mile...did they accidentally put oil in? did they put something in the oil which caused it? The ford place has it and quoute on quote said "what the heck did sears do there is oil overflowed" Please help