Right guys I'm not sure wether I've got a problem on my hands or im just being paranoid...

I got a new engine put into my Focus ST2 last week after the previous engine went tits up, I was doing general checks on my car tonight, water level was fine, oil on the dipstick looked fine but when had a look in the oil cap i noticed a dark brown goo on the cap, can someone please tell me what this is? as last time i had gunk in my oil cap it was a mayo looking colour and me engine blew up!


Cheers!