Dont know what to do for the best

Hi i am new on this sight and have resently brought a Rover 414 si 1996. Just checking the water level befor going camping last week and noticed a browny sludge in the water filler. Cleaned it out drained the water drove around for a few days but its still there. Now i guess that the head gasket has more than likely gone and needs changing. My question is because of a tight budget could anyone advise me weather to try a head gasket change by my self with the help of a haynes manual.

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