I have owned two M1A rifles for almost twenty years now, one since 1990 and one since 1991.
Both have fired rounds numbering in the thousands, both have been rebarrelled due to wear.
Both rifles use USGI componenets paired to Springfield Armory receivers, one uses Springfield Inc. barrel and both still have Springfield Inc. operating rods.
Neither rifle shows any signs of the receivers wearing out anytime in my lifetime.
The rest of the components can be rebuilt or replaced as needed.
This is the beauty of USGI rifles, they are designed to be rebuildable as needed.
The USGI parts that seem to be the most difficult to find for the M14 type rifles right now are operating rods and bolts.
Springfield Inc. is producing acceptable replacements for these parts now and their gas cylinders are excellent.
Sadlak Industries and Badger Ordnance produce excellent replacement pistons and operating rod guides.
Trigger groups can be easily rebuilt using M1 Garand components.
M14 type rear sights can be rebuilt using M1 Garand rear sight components and front sights are available from a number of sources.
There are still a large number of USGI trigger housings on the market.