I have an unusual problem with a leak around the cap on my front master cylinder. I removed it to add fluid, and now it wants to seep whenever I ride it. It does not leak when sitting or if I pump the lever. It only leaks when I take it out for a ride. It is only a small amount, but the stuff is so corrosive that any amount is too much. I ordered a new rubber seal to place under the cap, but it leaks the same as the original one. Has anyone any ideas as to what would cause this? The fluid level is right, and it did not leak before.