I have a 4 door 1998 Honda Accord EX and my mechanic told me I need to replace my camshaft seal, crankshaft seal and oil pump seal in my car. My question is does the engine need to be removed to install the new ones and does it have to be done professionally? My car leaks oil only when turn it off and park it.

 

Nope. Engine doesn't need to come out. It'll be more difficult to do while it's in the car obviously but it can be done. The oil pump also doesn't have a "seal" as it uses RTV in place of one, unless your mechanic was referring to a balance shaft seal. The timing components will have to be removed to do such a job and I wouldn't recommend trying it yourself unless you're mechanically inclined and know what to do. It would be a good time to replace the timing belt and water pump also if it hasn't been done recently.