Epoxy is your best bet if it can be worked INTO the seam. If the seam is too tight but a small seam is present use medium CA. DO NOT use accelerator. If there is no opening dribble in a LITTLE thin CA the entire length of the seam. Once the seam is tight go back and reinforce with tri-stock at all firewall seams using epoxy to attach. Finally, re-seal the firewall from fuel leaks. Use 30 min epoxy for this which can be thinned by application of heat.