Well, I would try regularly getting a boot log and look for the CS4231A device. If it is intermittently being reported as not found, then it could be the chip is on the way out. However, it normally tends just to go "phut" and lose all it's blue smoke.

If you are always getting a good 4231A and occasionally getting rubbish disk ID strings, then you may have bad IDE header joints. Either write down EXACTLY how the string appears, including funny characters, accent characters, etc. or snag the boot log with this on show. If you post that here, then using an ASCII table we can tell which data line on the header has got the bad joint. I can then tell you exactly which pin to solder to reduce the risk of damage.

However, I would STILL recommend that you do NOT DIY, and you pass it to one of the repairers such as Stuart at Eutronix, or myself. That way, you stand a better chance of having it survive ...