Common problem......your not the first...........New seals, yes!....CORRECT amount of 15w..........The K0-K2 models hold 220cc. K3 and up hold 150cc. '77-'78 F models hold 180cc.
Now........correct tiedown use..........as learned from ANKRA in 1973........Just snug the front straps about 1-inch of travel on the forks. Then install the rear set of tiedowns pulling forward and not very wide. Get them as tight as you can. Recheck the front but just snug. If you don't like the rear straps.......get a roll-on front stand from Harbor Freight or.....but still only snug the front straps.