Re: To flush or not to flush that is my question!
if you heard that "diesel noise" for a second after the car had been sat for a few hours it could simply mean the oil had settled in the sump. it takes a couple of secs for the oil pump to get oil back up to the tappets, and dry tappets are noisey. thats nothing to worry about.
i use engine flush every service on every car, always have and never had a problem in the past. on a high milage engine its not always wise to use engine flush because the deposits help to keep it oil tight and running smooth, if you clean the crap off you're left with larger clearances and thats when you tend to notice you start to burn oil. i've never heard of it causing leaks, but if a nice build up of crap was sealing a slight gasket leak then obviously removing the crap will cause it to leak. thats the risk you take, but personally i'd say its a tiny risk on engines will 100k or less.