Sounds like the early stages of oil cooler failure to me.
As others have said, complete and utter cr
ap. I do wish members with little or no mechanical knowledge wouldn't post totally incorrect information/solutions to issues that may involve other members in unwarrented work/extra costs. When a V6 oil cooler fails, you will see your coolant turn a murky brown - thats the correct and only visual sign of oil cooler failure. The oil cooler sits in the middle of the "V", immersed in coolant - the only place for a blown oil cooler to leak is into the coolant, no where else.
Think your garage took advantage of you and your limited knowledge re oil cooler failure on your car - certainly think they ripped you off financially

You will get better informed help/diagnostics on here, and certainly a more cost effective and correct diagnostics/repairs from some of the mobile mechs on here, or go to Serek's in Huntingdon for an honest, expert and cost effective repair service.