unless someone has retrofitted the unit with duo-cone seals, the 8u's are equipped with what the call "bellows seals" there is one on each side of the sprocket, two winters ago, cat wanted $900 a piece. florin tractor had NOS aftermarket ones for about 250. you need two bellows seals per sprocket. you will need 4 gaskets per sprocket, there is also a steel plate that the bellows seals turns against, you will need two per sprocket.
also want to check your final drive bearings, do this by sticking a long crow bar between the track frame and the sprocket. there should be zero side play in the sprocket. the bellows seals had a robust design and would leak if they had wire or twine caught up in them, more commonly i have found that the sprocket seals leak when there are bearing issues. There are some good conservation bulletins posted by Josh on this forum, there are also some threads about repairing final drives on d6's on this forum, and a fairly in depth thread on the ACME site.
http://www.antiquecaterpillar.info/index.php?/topic/20358-ressurection-of-d6s/
when you fit direct electric start to these older cat motors even in warm Australia they don fir strait away and I was taught you never wind them over with the fuel on as it miss fires and can damage the starter and ring gear wind them over for say 10 seconds on full compression with the fuel off then just open the throttle and they fire right up
Having said that I dont know whether that would work any good in your part of the world in winter
Paul