Hello I have just noticed several amount of oil leakage at the left fork.

What should I do?

Drop the forks and change the oil seals. Nothing else you can do really.

I assume you mean by "several", it's losing a lot of oil? Topping up the lost oil would keep your damping going as a stop-gap, but it will be almost impossible to gauge how much you've lost/need to put in and the problem is only going to get worse.

Best get it fixed.

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When riding enduro or motocross the fork legs get very dirty and some times the dirt get trapped in the oilseals on the forks. A quick fix for this on the field is to use a thin feeler gauge between the fork legs and seal to clean out the dirt. This will stop the oil leak some times, unless the seal is broken.

You need to service the forks anyway because the dirt has polluted the oil and some of it is missing. But it will let you finish the the route or get home.