No.
Rubbing alcohol / isopropyl to clean the barrel.
Silicone grease (not oil) to lube the cylinder.
Some thick lithium grease for the gears.
Soapy water to clean the rubber when they are out of the gun.
Teflon based spray or dry silicone for GBB internals.
Define klonk. Preferably with a video.
The piston returning after releasing the trigger is a small "clack". If the anti-reversal latch is missing then it's a longer sound as the gears move the motor.
It seems you do not have a deep enough understanding of the internals of the AS guns. The best is to bring it to an AS mechanic to fix it. You can easily make things worse or buy and try a lot of expensive parts before finding the problem.
The site is great, I've ordered quite a few times from them. They are moving warehouse that's why the price drop. Shipping for the stuff on that high discount is really high as mentioned before.
I agree with Duck. Either something is high speed in it or the lipo is 3 cells or the rof measuring thing is off.
Not that it matters. If it fires fine then it's great.
If you have a compressor - not just air duster - then wash it in very soapy hot water first. Submerge it brush it, etc. Then remove the water with the compressor and then relube it.
Receiver pins:
http://shop.ehobbyasia.com/king-arms-reinforced-receiver-pin-set-for-marui-g3-series.html
http://www8.wgcshop.com/wgc2008/main/product_detail1.php?search_From=searchItem&item=KA-PIN-02&search=special&rs=g3%20pin&catid=&cat=&view_choice=a
Front pin I think
http://www8.wgcshop.com/wgc2008/main/product_detail1.php?search_From=searchItem&item=ELE-OT0412&search=special&rs=g3%20pin&catid=&cat=&view_choice=a
But it's not worth spending on this. I would just get some black screws to replace them. I think they are 6mm.
Ukara / VCRA is UK only. Hobbyking is china, so they probably don't know about it / don't care. Usually their shops state that it's your responsibility to deal with the customs of your country.
Hope that the customs will want to ask you about your defence instead of just destroying your stuff.