Is the weather hot (consistently warm air) where you live?
Previously, I announced my GameCube unit (bought at U.S. launch) died, but it turned out it wasn't gone for good. When I reported it, I was trying to use it at my apartment outside of Sacramento, where the temp was 96-F (and up) earlier in June. It's poorly airconditioned, and the outdoor air was warm enough that you don't want your windows open. The indoor air is noticeably warm, and also poorly circulated.
When I used it while in the Bay Area 3 days later, with the temp in the 80's-F and below (considerably cooler and more comfortable), it worked like a charm again.
The past couple days, the Bay Area's having a heat wave, with temps 95-101-F all around, and my system started acting up with the same read errors again. I then pointed an electric table fan toward it to help provide fresh air and cool the plastic shell (especially the hotter exhaust-side), and to my amazement, it achieved stable performance again.
Apparently (with my unit), over time the internal components lost their stability and became more susceptible to heat-related breakdown, where "something" decides to "quit" when the system reaches a certain temperature. I don't know if the GC case fan is under-performing, or if there's a mechanical disc drive error or an electronic error due to the heat. But overheating is definitely the problem.
For now, I'll stick with the $10 table fan remedy and do whatever I can to avoid sending it out to get it refurbished for $70.