Head gasket blown

Unfortunately, if they ran this test for combustion chamber gases in the cooling system and it failed then you do need to replace the head gaskets.

https://www.2carpros.com/articles/head-gasket-blown-test

Eventually when the leak gets back enough it will allow the coolant and oil to mix which is talked about in this guide:

https://www.2carpros.com/articles/coolantantifreeze-in-the-engine-oil

You can try using one of the chemical sealants but a lot of times they cause more issues and could plug the heater core. However, we did do a review of the leading brand so here are a couple videos:

https://www.youtube.com/watch?v=Xi41RFMP8Ow

https://www.youtube.com/watch?v=iuEVLFEF0AM

If this does not work or you just want to fix it, then you will need to replace the head gasket. You will want to do a cylinder leak test or at least a compression check to find out which bank the issue is on.

https://www.2carpros.com/articles/how-to-test-engine-compression

I attached the process below for the left head as the right is similar. Please let us know if you have any questions. Thanks