I think that's something of an exaggeration. I have an OM1n and three OM2ns (and other OMs), and only the OM1n has had a CLA. The OM2ns are working just fine (and should one of them fail, it won't be worth the cost of a CLA - I'll just throw it away and buy another, they're so cheap).
Well, maybe but with a CLA from someone like John Hermanson you're good to go for another 25 years.
I have a 1 that works great and it is doubtful you'd find much meaningful difference between the versions. I'm going to go with the CLA recommendation. If the camera hasn't been CLA'd then it is pretty much certain that the prism foam has degraded and damaged the prism silvering. That is really not a big problem as the polished glass reflects well by itself. Polish the glass and feather the edge of the silvering with a mild abrasive such as toothpaste, and you won't even notice the damage. I believe having seen that an OM-10 prism will fit, but don't recall exactly. Either way, once it is fixed up it will be a joy for many years.
There were a number of incremental changes in the design and construction of the OM-1 over its production life. All of those changes were incorporated in the OM-1n.
I think you will find that repair people like John Hermanson will recommend the OM-1n.
In addition, the OM-1n shares the Hot Shoe 4 with the OM-2n, although Hot Shoe 4's in undamaged condition can be hard to find.
“Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”
Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2