Tom Rahochik also advised me to check the turbo oil drain back hose and clamps. It turns out that I had the wrong type of hose material and the wrong clamps. This became quite a research project because Chevy used three different types of clamps through the years.

The clamps proved very challenging to find. Tom was able to come up with one for me and then local club member John Barnes came to the rescue by finding one in his miscellaneous parts box, no doubt from an engine he had parted out or serviced years ago.

Finding the correct hose material was also challenging. Fortunately, local club member Dan Davis had a sample (on his very original '66 turbo coupe) of both the hose and the clamps, and Larry Claypool had a source for the hose. I'm really glad we replaced the hose, because we found that the existing hose had too large of an inside diameter, and was dripping.

This photo shows the correct hose and clamps after installation. Thanks to Duane Wentlandt for helping me with that job. It's a very tight fit, and he has a special open-end wrench for reaching one of the fittings.