MacBook Air & white macbook assistance

I've just finished an upper case repair on my air, all went well apart from a missing screw and I'm uncertain the gasket at the fan is seated exactly as it was before plus it was stuck with adhesive to the fan casing...is this gasket very important in terms of positioning, anyone know what size the screw is, m1, m2, etc...see section 9...

https://www.ifixit.com/Guide/MacBook+Air+13-Inch+Mid+2011+Display+Assembly+Replacement/6361

I'm also trying to determine the model number of a white 13 macbook it's late 2009 by the serial number, W8950uxd8pw, but I need the model number, Is it maybe a1181...?

Kind regards

An Apple model lookup site says it is an A1342. I bought a tool kit for Apple products when I want to blow out my MBA. If it wasn't for Mr Fixit's website I would swear it doesn't have a fan because I have yet to hear it.

I don't know the size of the screw unfortunately.


EDIT: This the website I found the info on:

http://www.powerbookmedic.com/identify-mac-serial.php

Thanks...

I am hoping to get a faulty trackpad sorted on this white macbook but I've seen no guide on how to do just the trackpad. Although I'm seeing separate trackpads on eBay. Usually when you don't see the trackpad being done it means it's a specialist job that requires cutting, heating, etc