The rear main engine seal should not typically be leaking on a 2004 truck with 95K miles on it. As long as there is no oil showing on the driveway, I would not change it out at this point. However, for peace of mind, I would get a rear seal and an oil pan gasket to carry with me so that if I did need to get it done, I would have the parts necessary for any competent mechanic to do the work. You might want to look up what the exact procedure is to change the seal so that you know what parts are required. Some can be changed by dropping the pan, but many others need the transmission removed. Might be additional parts required to complete the entire job.
Just as an aside, I had a weep on my transmission output shaft seal and it lasted for 3 years until this spring when it suddenly let go with a vengeance!!