I have used an engine oil and PTFE based fuel additive after my then new 360 GLT had covered its first 10k, giving the engine time to run-in. Also used the oil treatment in the diff and gearbox. The car has had an engine oil/filter change every 10k. The oil in gearbox and diff has never been replaced only topped up when necessary.
A few years ago when changing the spark plugs a friend checked the cylinders with an inspection camera. You could still see the honing marks in all cylinders. The compression was good as new. On the highway with two passengers the car still returns 6.3 l per 100 k. The 360 has covered over 850,000km without removing the head or had any work done on the gearbox or diff.
BUT, I believe that "snake oil" is being sold, so be careful of additives, use only very well known and long established brands of engine oil and fuel treatments.
i have another 360, which to my knowledge has never had any oil additives. This car has covered about 450k and I'm considering an engine rebuild soon as it is using oil and the bearings are getting a bit noisy.