There is oil mixed in with the antifreeze fluid in my radiator. Why? on 1995 Isuzu Trooper

I recently had a neighborhood mechanic replace the power steering pump, altenator, and radiator fan in my Trooper. Also, he told me my transmission is starting to go bad, and did a "transmission tune-up". My theory is that some mechanics SAY they know how to work on foreign cars, but end up experimenting instead. Could he have done something wrong?

Asked by for the 1995 Isuzu Trooper
IF auto trans.,possible radiator trans. fluid cooler is defective, fluid leaking into coolant there! And may cause transmission to act up. Can easily be tested. See a repair shop or trans. mechanic. This cooler is inside the radiator.
Thank you, guys.
U bet.
1 more answer , 1 more comment
Might have a problem with engine block maybe a crack. I would flush radiator system out again.
Thank you.