If the top end job was recent you may just need to re-torque your head bolts. Loosen that bolt that attaches the cylinder to the frame and torque your head bolts in the numbered order that is stamped on the head. Don't know what the '85 torque value is but likely somewhere around 25 ft-lbs.
Your silencer should be able to be repacked. Most of them can be and the packing material is less than $10.
1983 ATC 300R (Hondaline kit)
1985 ATC 310R (CT Racing)
1986 TRX 250R (Bone stock)
1988 TRX 330R (ESR)