Thank you all for the useful information. Let me be more specific my situation.

Since the Ford here in Taiwan does not provide any parts of Escort Cosworth, it's really hard to get geniune parts here. Especially I plan to have a fully paint job and engine rebuild for my Escort, so the items like windshield, rubber strips, pistons & rings, engine wiring looms...etc would be necessary.

So, would it be better to buy from a mainly geniune parts dealer rather than a tuning shop?(I guess so.) What is your solution if you guys need kind of parts I mentioned above?