Help!GL Hatchback Check Engine Light

Hi everybody - I have just bought an '88 Subaru Chaser, known in the US as a GL Hatchback. Its in great shape, no rust and only 76000 km. It runs great but the engine light comes on occaisionally. The dealer I bought from had another one which he sold to his friend and he is having the same problem. I am wondering if this is something that happens with this model. The mechanic I bought it from doesn't know why - niether does the mechanic at the Subaru dealership across the street. His (the Subaru mechanic) solution was to replace 5 different things that would cost about a grand.