Hey, mine had the same problem when I bought it. Went to Lim Ah Boy to change oil seal, the mech told me that the front fork were broken (just rusty, that should be the cause of the damage of the oil seal), then I had all of them replaced there at about 80*2(front fork tube)+40(oil seal), can check should I still have the receipt.
Edit: I think it's a damn expensive replacement...