We bought a house with an old (1985) Pulse furnace. It was recalled and repaired in 1995 and a new plaque says 1995. Am I safe in assuming my furnace is really 18 years old, not 28. It is working well but unsure if I should be looking for a replacement.

If it ain't broke, don't fix it.

1985 or 1995, it should be inspected & tested by a professional with the knowledge & tools to do the job properly.