Terrible. 99.99% of the time you always want to run the most current version of your OS of choice. Sacrificing security for performance is stupid.
Advise the customer that they need to throw $20 at their machine if they want to keep it on the road. Although I'd also feel obligated to say that the money they're spending on repairs and memory upgrades is not actually going to FIX anything, and spending $50 here or there to bring it into the shop is great for my business, it's just wasting their money. They really need to start thinking about a new computer.