you are doing so few miles i wouldnt be to suprised to find the oil filler looking a bit creamy and it would seem you arnt realy going far enough to geting the engine properly warm to test you head gasket worry if i were you i would fill the radiator brim ful and leave the cap of and let it tickover and watch for bubles apearing in the radiator to test the head gasket also if you were geting water in the oil you would notice the oil creeping very slowly up the dipstck over a period of time if you do see noticable bubles in the water then you need to do a compresion test as at least one but probably two would be down you say it drives well so i am thinking that as 2.5s dont make many ponys you probably dont have any probs as you would notice any loss of the power you have