If you detect signs of oil leaking through the camshaft oil seal, first check the crankcase ventilation system for blockages and pinched hoses. Repair if necessary.
If the oil leak persists, replace the oil seal.
You will need all the tools necessary for removing the timing belt (see "Replacing the timing belt and engine pulley on a Renault Logan"), as well as a 16 mm wrench, a screwdriver, pliers, and a hammer.
Disconnect the negative battery terminal.
Remove the timing belt.
You don't have to remove the belt completely; just remove it from the camshaft sprocket.
Loosen the camshaft sprocket bolt while holding the sprocket from turning, as shown in the photo, using pliers and a ratchet or large screwdriver inserted into the pulley holes.
Remove the bolt from the camshaft hole.
Remove the pulley from the camshaft end.
Pry it off with a screwdriver. Remove the oil seal from the cylinder head housing.
Before installing a new oil seal, inspect its sealing lip.
It should be smooth, without tears, dents, or rubber buildup.
The oil seal spring should be intact and unstretched.
Lubricate the sealing lip with engine oil.
To facilitate pressing the oil seal in, chamfer its seating lip slightly using a file or fine emery wheel.
Install the oil seal with the sealing lip facing inward into the cylinder head socket, carefully push the sealing lip onto the camshaft (for example, using a wooden stick), and press it in until it stops using a suitable drift.
You can use a suitable-sized socket from the tool kit or an old oil seal as a drift.
Reinstall all removed parts and assemblies in the reverse order of removal.
Install the camshaft sprocket with the protruding part of the hub facing the engine.
Tightening torque 45 Nm (4.5 kgf-m) camshaft sprocket bolt.
Adjust the timing belt and accessory drive belt tension.