2000 Subaru Outback Check Engine Light Problems

I've having issues with the check engine light on my 2000 subaru outback. The light has recently come on, and is blinking. Before that it was going on, and then going off. It's driving me nuts, and it's been in the shop just about every month since May. The car has 82000 miles on it. I've already replaced all the head gaskets and one of the censors, and had all the fluids changed, the battery is the same battery that has been in the car since it was purchased in 2001, and there are problems with corrosion on the cables, and sometimes the car has starting issues. It's not making any weird noises, runs a bit rough when you step on the gas, and that's about it. I've even hooked up a code reader and nothing comes up. So if anyone has anything that would be helpful for me I would greatly appreciate it. Thanks. -Jen