One of my co-workers has recently suggested using 1/2 to a full quart of transmission fluid as engine flush during lube oil change. He states that it thoroughly cleans and flushes the top end of an engine to nearly a brand new look. Has anybody else heard of doing such a thing and/or does anybody have any insight on if this is good for the engine or will it do more damage than good? For those of you who do use transmission fluid do you suggest normal fluid or synthetic.