Bombardier makes an oring kit for their 1983 and later model trim units. About $23. Part number 393942. Very possible that this kit is the same for your 79. You can compare orings by checking out the online parts lists from Bombardier at: epc.brp.com.
I have a 1979 85 hp johnson outboard too.My motor has a leak in tilt and trim.I bought the seal for 77 cent on sierramarine.com.I fixed it today and put new trim oil and it worked perfect.So this is a good sugestion.
Any repair kit should be OK for the trim cyls. Looks like OMC used two different mfr's for the tilt cylinder that year, so you have a 50% chance of getting the right o-rings for that cylinder.
