The first picture shows the two studs under the oil cooler – with
one missing. Those are case halve fasteners that straddle the
#1 main bearing. The two studs are threaded into the 1-2-3 half
of the case.
One thing I note is someone has used a regular nut. These are
supposed to be cap nuts. Oil will simply spiral down the threads
and leak. I suspect someone tried to tighten them too much to
stop the leak and pulled the threads.
A major issue is the space between the body of the stud and the
case is used to carry pressurized oil to the main bearing. This
stud feeds the #1 main bearing and then to the internal
passages in the crankshaft to the rod bearings. you won’t be
able to Helicoil without getting chards in the passage that feeds
the #1 main and the rod bearings.
(C) 2003 Wayne Dempsey,
How To Rebuild & Modify Porsche 911 Engines
Here the red arrow is the passage feeding the #1 main bearing.
The violet arrow is the through hole for the now pulled stud.
Note that the two intersect.
Short answer; I don’t see how you can Helicoil this without
contaminating the oil system. The case has to come apart.
Best,
Grady