RepairPal Certified shops can diagnose and repair your 1992 BMW 325i. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
Take a look at www.alldatadiy.com and for $26 you can get access to the factory manual online for a year. Once you read through the repair steps, you can decide for your self. Most heater cores on BMW are not easy. I have done a few. Good Luck!