Need opinions/ advice head gasket problem

[wrxer18]

Hey guys i have an 02 bug eye with about 134k on the clock. The motor was rebuilt around 95k from the previous owners due to a radiator failure that happened and the dealer ship rebuilt the motor. The other day i had my spark plugs and coils changed and the mechanic told me that he found some residue on the spark plugs that looked to be coolant. He said this MAY be because of the head gasket and it may be leaking slowly... Now i hope this is not the case, but if it is leaking slowly how long can i drive with it like this? I am thinking of selling it and getting a brand new suby now, but this wont happen for at least 6 months. Will i be able to drive it for that long if it does have a small leak? also how do i check if it is leaking? The mechanic told me to mark the coolant level and check daily to see if it's getting lower. any advice would be great thanks!