Some white smoke from the breather tube on a 20 year old engine would be considered normal by most mechanics. At 130,000 miles, your engine should have at least 1/2 to 2/3 of it's life left. If oil consumption or coolant loss is not a problem you should be good to go. Some 3208 engines do have head gasket problems, but that will not require engine removal if your's ever fails.
Look closely at your rear cap, there should be a joint where the lower part is removable. The seam is usually in the engine access opening where the lower part of the opening can be removed with the lower fiberglass panel and it is usually covered with a seam sealer that is even painted on occasion, however I have never tried to remove the panel on a 1990 Marquis.
Gerald