overheating on 1999 Cadillac Catera

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
99 cadillac catera overheated and water that come out of resevoir left an oily residue. Blown head gasket?
(2) Answers
(1) Comments
very likely. get it leak down test to confirm.

Is this something I can do or do I have to take it to a mechanic to get it tested.
Bad coolant/oil heat exchanger. Common problem.