Engine flushing is a good thing to do but not so often and also the main concern to do flushing is about the engine seals...ideally and theoretically its good to have your engine flushed with the help of oil or diesel but if the engine condition is apparently poor then flushing can cause serious problem like engine oil leaking from seals... you know sludge itself is a good sealant some times it is serving as a seal where the packing is weak...and when you get your engine flushed sludge would go and hidden problems would arise...
so conclusion is try to avoid flushing if you feel that your engine has almost complete its life and you are in no mood of getting it overhauled in the moment...
good practices are given under...
- despite of getting flushed your engine, try to go at such oil shop who has a ditch or a hydrolic lifter to lift you car exactly vertically, try to avoid the Slope Arrangement as it results in old oil accumulation in oil chamber.
- after oil drain ask the service man to blow compressed air in the engine. that shall help to eliminate any deposited sludge particles in oil chamber and engine.
for the oil, i must say all engine oils are good provided they are original company oil (not the badami bagh 2-3-4 # oils)
i used Total in my alto and i was satisfied, i used havoline and found it good as well, i used zic hiflo one time but it was my bad luck that oil was 2 # and i ended with a blown out engine. currently i m using gaurd oil and it is good as well...but don't know why, for no reason i have no trust on Shell