I had a similar leak about a year ago, it was one of the plastic side tanks on the Rad. If you only have a slight seep, I would just make sure you have plenty of water to replace any leakage, but I would be reluctant to put any sealant in the system. On my S4 it was a pricey job as the wings and cowl had to come off for access. Also hope a replacement Rad is readily available. Best of luck.
