My Mac partition keeps failing requiring a clean install every few months. I've periodically scanned it with Onyx and do permission fixes and repair disk using the Mac OS X install disk. Over time, I can't repair the disk and told to reinstall the OS.
Anyway, are there any free apps that I can use to check for disk errors?
I'm using a 2011 iMac w/ a Samsung HD. So I'm not part of the Seagate recall group.
Check the drive's S.M.A.R.T. status in Disk Utility. If it's not "Verified", replace your drive ASAP. You can also try SMART utilities like SMART Utility or SMARTReporter, which will give you additional information about I/O errors and bad sectors.
It sounds to me like the hard drive is indeed on it's way out. I would suggest replacing the drive and then, on a PC, should one be available to you, run SpinRite on the drive. SpinRite will do a complete scan of the disk and make the drive stable enough for you to recover any files you may need off the drive.
MacBook Pro 17-inch (Torako): Intel Core i7-2720QM; 8GB DDR3; Intel HD3000 / AMD Radeon HD 6750M; 240GB HP v300a SSD; 17-inch LED Backlit WUXGA; OS X Mountain Lion IBM ThinkPad T40 (Lilica): Intel Pentium M 1.5GHz; 512MB DDR; ATi Radeon 7500; 80GB Fujitsu HDD; 14-inch XGA; Windows XP Professional Desktop (el Gigante): AMD Phenom II X4 965 Black Edition; 16GB DDR3; 128GB Samsung 830 SSD; 1TB WD Green; AMD Radeon HD 7770; LG Flatron E2742; Windows 8 Pro x64