How long do camshaft seals last?
around 80,000 miles
Camshaft seals are usually located on the top of the cylinder head towards the rear of the engine and near the firewall. When they begin to leak, there will usually be traces of oil on the rear of the engine right below the valve cover, which can sometimes flow to the edges or corners of the engine.
Beside this, How do you know if your main seal is leaking?