My pleasure Dear and you are always Welcome.
All Praise and Glory is for ALLAH ALMIGHTY Only! I am nothing. 

If he goes for rebuild / overhaul, then mechanic must be expert, and should give him warranty of xx thousand Kms / xx months., and if he'll be an expert, he'll not refer 20w-50 to him, rather 10w-30 or 10w-40.
And if he suggests him 5w-30 after rebuild / overhaul, then indeed he is a true and confident mechanic, and knows what he is doing! 