Better than oil additive , use a premium quality oil, such as Dexron III (H) for your car.
High quality oil do not need additive because they have some yet. Adding others may have wrong effect and some unwanted consequences.
Oil level : never cold, but hot after driving minimum 20 km,with engine iddling on park
You should check again, you may have too much oil which is very bad.
Good idea in any case to drain oil and clean filter. If oil is dirty and smell, you may have ta change it 2 or 3 times
97 Continental R