As vehicles get older, it is not uncommon for seals and gaskets to start leaking. Replacing these is fairly common. Whether you replace it now is up to your level of frustration with how big of a mess this will create, not only on and around the engine, but ultimately on your garage floor or driveway. It is not an emergency for your engine, as there is plenty of oil stored in the crankcase of the engine. However, if you choose to wait on getting it fixed, you will need to ensure you keep up with replacing the oil which is lost through the leak. With a slow drip of a leak, it would take a long time for all of the oil to leak out, but have no fear, it will leak out. If you keep up with the lost oil, there is no fear of collateral damage to internal engine parts due to this, though. Keep the oil between the high and low marks on the dipstick and you're golden.