Do yourself a favor and have that furnace removed. Do not throw any more money at it. The service company should have already made that suggestion. That furnace was absolutely the cheapest furnace built in 1990. I believe the recalls mentioned were for plastic flues that were used on this model.
This furnace is going to keep costing you money. It is a very bad investment. I am not saying that these furnaces are junk, they are not but it seems that the one you have might be. Furnaces don't last as long as the older models.
Get yourself a 90+ furnace that uses outside ait for combustion. It will payfor itself quickly in gas bills and repair bills that you will keep having with the older furnace.