Synthetic oils

I need to chime in here.
I do have a lot of experience using synthetic oils and greases over the years.
Namely Amsoil.
There is not a better synthetic product out there than Amsoil. Period.
Any full synthetic oil is a good idea, but i had the best results with Amsoil. (I am not a dealer BTW!)
Synthetics should not be used on worn out parts or engines with the hope that they will make them better. Synthetics work well with good engines, and parts that are in good condition. A common myth spread by dealers is that they will "magically" save your parts or engines and that is not true.
2 stroke oil:
20 plus years ago i used to race motocross with 2 stroke engines, and the manufacturer recommended 20:1 mix. Bel-Ray was the big deal at the time and they recommended 40:1 and all of the big name racers used it. Amsoil 2 stroke oil was recommended at 100:1 and i used that, i had to jet the bike down a lot, and i never had a problem with engine failures at all, on the contrary, i went a whole season on one spark plug, and at the end of the year, i tore the engine down and it was still like new inside. The bore was measured and no wear on it at all. I rode the bike for 3 years with the same results.
Gear oil:
Specifically, i bought a gallon jug of the Amsoil 75w90 gear lube. At -40 i left the jug out all night and i was able to pour it easily, like engine oil. I used it in a Dana 60 in my '69 Super Bee with the clutch style sure grip with no other additives and it always locked both tires with no chatter or noise, i had the car for over 15 years, and it never changed. The oil still looked like new when i sold it 7 years ago.
Grease:
Back in the late '70s, my dad drove a truck for a living. He put on about 400 to 500 miles a day. My job after school was to grease and service the truck in the evenings. We would go through u-joints every 50,000 miles or so with conventional grease, and i would pump in 6 to 8 shots a night into them. Water and crap would come out of them every time. We switched to Amsoil grease on a new u-joint, and they lasted at least 5 times longer, and when i greased them, no water inside and only one shot to come clean. Same for the kingpins, steering, etc.
Engines:
My brother bought a new '78 GMC 3/4 ton pickup 350 auto. After break in, it was switched to Amsoil synthetics all around. He changed the oil every 10,000 miles and the filter (Amsoil) and he drove it 150,000 miles before the engine was pulled to put in a 454. The engine when pulled apart to be reringed and sold had no sludge in it, and was very nice inside with only slight wear. An easy re-ring job. Even the cam was reused, with no measured wear. How rare is that for a '70s small block chevy?

The bottom line is that i'm sold on synthetics, especially Amsoil, even if it costs 4 times the price of conventional oils and greases.
Good proper maintainance goes a long way too.
Just drive in the cold weather and feel how stiff the vehicle is without synthetics, as opposed to with. (we're talking -40 here)
You'll be sold.
Amsoil's not worth it you say?
Convince me otherwise, all of my experiences were before they were marketed heavily, and they are as good today as they were then if not better.
Just my 2 cents as always,
Tom.