No seals are needed to replace the harmonic balancer. As mentioned, the bolt is 15/16". Check the service manual for bolt torque.
You will need a harmonic balancer puller to remove the balancer. Remove the balancer bolt all the way and be sure to get the big washer out prior to installing the puller. Examine the puller pilot end that bears against the crankshaft to see that it does not ride on the threads. My balancer puller has a big pointed pilot that rides against the crankshaft end without getting near the threads. If the puller pilot does ride on the threads, then you will need a couple of washers that will fit inside the balancer bore so that the puller pilot has something to ride on. You can use the balancer bolt instead of washers, just be careful to leave about 5-7 turns of threads screwed into the crankshaft.
This one is from AutoZone, and it looks like the pilot end will protect the crankshaft threads. AutoZone OEM27019
You will need a harmonic balancer puller to remove the balancer. Remove the balancer bolt all the way and be sure to get the big washer out prior to installing the puller. Examine the puller pilot end that bears against the crankshaft to see that it does not ride on the threads. My balancer puller has a big pointed pilot that rides against the crankshaft end without getting near the threads. If the puller pilot does ride on the threads, then you will need a couple of washers that will fit inside the balancer bore so that the puller pilot has something to ride on. You can use the balancer bolt instead of washers, just be careful to leave about 5-7 turns of threads screwed into the crankshaft.
This one is from AutoZone, and it looks like the pilot end will protect the crankshaft threads. AutoZone OEM27019