There is a vent tube for the ATX sort of below the battery. The flasihing OD light means that the computer has detected something wrong with the ATX and will have a diag code stored which can be scanned at an auto parts store. This is usually pretty bad news.
A check of the fluid level and fresh change of fluid is probably a minimum remedy although it may not help. The Lucas ATX fluid conditioner may be a temoporary help until the tranny can be repaired/replaced. I know some GM owners that have had good success with this.
