vibrates and I don't know why.

There are a lot of things that can cause the seals in your engine to start leaking. First, simple wear and tear can cause the inside of the shaft seal to wear so much that it will start to allow oil past it. Low oil levels can also accelerate this process.

Oil leaks are the most common symptom of a problem with the crankshaft seal. If the crankshaft seal dries out, cracks, or breaks, it can cause an oil leak. Small leaks can cause oil to accumulate on the undersides of the engine, while larger ones may produce a drip of oil from the front of the engine.

The camshaft seal is used constantly, which will usually lead to it wearing out over time. The camshaft seal is made to last for around 80,000 miles but in some cases, it will wear out prematurely due to damage to the camshaft. The heat that the engine produces can lead to the seal becoming damaged over time.

The front crankshaft seal located in the front of your car's engine and is designed to hold oil from leaking as the engine is running and the crankshaft is turning. ... If a leak is detected check above the seal to make sure oil is not leaking from a higher point and making it look like the seal is leaking.

If the engine appears to function normally, as before, it is likely OK to drive it. However, if the engine starts to misfire (you would see a flashing check engine light) then it is NOT OK to drive it all without risk of damage. Diagnostic Trouble Codes can never be used to "directly" condemn parts.