1996 5.7 vortec timing cover gasket

If you mis-wired a light switch would you be angry if the customer called you back to fix it? Would you try to charge them for correcting your mistake? I ran into this too as a tv repairman. Sometimes you think you repaired an intermittent problem, then find out the problem is still acting up. The only exception with your mechanic would have to do with who diagnosed the leak. If you did and asked your mechanic to replace the timing cover gasket, it would not be his fault if the wrong part got replaced. If he diagnosed the cause, he was either incorrect or, as you suggested, put the new gasket in wrong or it got damaged. In those instances he can be expected to clean the area and re-diagnose the leak at no charge to you. If a different problem is found, you could be expected to pay for the parts, but very often the shop will cover the labor, especially if you are a regular customer. At the very least, give your mechanic the chance to check his work. The last thing he wants to find out is someone else had to come behind him and fix the problem. One tool that works well for finding leaks is a smoke machine. You inject white smoke at 2 psi into the dipstick tube, then watch for where it comes out. That should be pretty easy to spot for a leak as big as you described. The timing chain cover could be cracked or the oil could be running down from the front of the intake manifold.