I have a y t6700 and a yt 6800 , had to replace the seals in both just last year. the heat just cooks the seals over time. just replace the seal and you will be fine. Get a oem seal from Yamaha is what I used.
pulled clutch and pulley off removed engine , then replace seal. You need to have a special puller to get the pulley off. do a search on here there is a post on how to make a puller using a bolt and a spacer rod. to get pulley off.
on my 6800 i did not remove the engine. removed pto then pulley. installed seal then reassembled pulley and pto. hardest part was removing the pulley. with good pulley tools and common sense it's not that hard. it's also a good idea to have the pto rebuilt. 2fastforyou on this site can do that very well. Denny
i used a pretty big chisel that was tapered and used it as a pickel fork and hammered it between the pulley and the metal part on the case. did not have to remove engine. just spin the pulley around in several places and smack it between the pulley and bottom case. you will see a metal part on the bottom of the case and thats where you should place the chisel. you should e-mail 2fast4u on this site and ask about rebuilding your pto. he modifies them which makes them better. was only a hundred bucks which is much cheaper than a new one and you have the original one that came with for a perfect fit.