The sooner you explant a leaking silicone implant the better. Once your breast tissue deflates, the skin envelop contracts, changing the shape of your breast even if a new implant is placed (bigger problem with saline implants). Older generation silicone implants are problematic because they are a sticky gel that starts to migrate in your tissue. Once that happens, it is impractical to go searching for those migrated particles to remove them. The newest generation implants are designed to maintain their shape even after rupture so silicone migration would not be as much of a concern.
Generally, insurance does not cover this complication of breast augmentation. Having said that, I have had a patient where the HMO has agreed to cover this procedure. If you were enrolled in cosmetic insurance at the time of your surgery, that may cover it as well.
Depending on when you had your breast augmentation surgery and which brand of implants were used, the implant company (Allergan or Mentor) may have some sort of insurance policy where they replace the implants for free and give you a stipend to help cover the cost of surgery.
The best thing would be to check with the plastic surgeon who performed your breast augmentation surgery, have him examine you, and discuss your options with you.