What is the value of a 1955 US 5 dollar bill that is missing the red or green seal?

Please check the date again. The US didn't print any bills dated 1955.

Error bills are difficult to evaluate sight-unseen because there are different possible causes for the error. For example, the seal could be missing entirely or it could have been printed on the back of the bill. In any case these errors generally sell for in excess of $200 to $300 depending on the bill's condition, so an in-person evaluation by someone who works with error currency would be needed in order to get a more-specific value.