It is not unusual for a 16 year old car to start needing this kind of attention. As in most modern cars, many of the operating parts are physically covered. In order to trace something like an oil or water leak those covers have to be removed. It’s mindless work but it’s still labor you pay for, and it’s in your interest to make sure you only pay for it once. I’d recommend finding a trustworthy mechanic to look at it and give you an assessment. Whoever you used for the oil pan gasket might be ok, but it’s hard to tell from the history as presented. If the front main seal is involved expect to be advised to replace the timing belt and water pump. Be ready for a bill approaching $1000 (mostly labor) and be thankful it’s not the rear main seal that is leaking.