My son has a 1993 GMC Sierra 1500 with a v8 350 in it has about 125000 miles on it no problems at all until he went to walmart to get the oil changed for the 2nd time he had no oil leaks at all now 3 days later truck is leaking oil he took it back over there for them to check and all they tell him is it looks like the oil maybe leaking down from the top of the motor it could be a gasket or a head gasket ok like i said up until then no oil leaks or any thing also when he went to check fluid in radiorter ( Sorry spelling) it was low Please help what can it be? thanks>