My theory on rear main seals is simple; you are already there, change it. Why do the work twice when it starts leaking in the near future. As far as just tightening the cover bolts, waste of time really. Once those bolts loosen up, even just a tiny bit, the seal between the cover and block has been broken. There is no way of fixing it without replacing the sealing material. Do it right the first time and you never have to worry. Im of the pursuasion that I would replace the trans input seal as well, but thats just me. Taking things apart disturbs the way it has meshed with everything else for years. It will never be reinstalled in the exact same way it originally was so stresses are minutely changed on all the parts involved.
Take it from a heavy equipment tech that has learned these lessons the hard way.