Overflow pressure bottle

Just providing a bit of feedback and after advise since changing the radiator presser bottle in my 06 4.2tdi patrol
First of all the factory one was buggered so I ordered a replacement. Decided to go with dayco as it was slightly cheaper. Fitted it, filled with coolant, no issues. After a week I took the cap off to top up. Turns out the cap doesn’t seal! It looks like it does but give it a slight wiggle and it pops off. Ordered another with the hope of returning this one and it’s exactly the same, the cap does not seal correctly!
I then ordered genuine and no issues at all, seals perfectly. So if if your in the market for a new one, stick with genuine!
This is where I need advise. After installing the new genuine one, I noticed that the relatively new dayco one had accumulated rust at the bottom of it. It was only in for three weeks. When I say rust, it was just a brown liquid on the bottom of the tank. Should I be concerned about this?


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