My experience with Motorclean Islamabad has been very positive.
Its one of the few places who wouldn't force/trick you into cleaning or changing your CAT unless necessary.
As for used parts, its definitely possible to find cheaper used parts if you're willing to risk the outcome. You may get a pearl or you may end up with a lemon. And if Rwp scrap market is anything like Lahore's Bilal Gunj, try asking for a refund or replacement for a part you installed in your car.