We have a Miller Kerosene Mobile home furnace. It runs fine! However after the burner shuts off and the blower is still on we smell burnt kerosene. I went outside while it was firing and the smoke is clear but the chimney cap is all sooty. We have noticed a thin black soot on the appliances in the house. I checked the peep hole door on the furnace and it is closed. The unit has been serviced every year including this one. I am concerned it might be a cracked heat exhanger box. Please help!!

You are giving the classic symptoms of a cracked heat exchanger... you can usually only see the small cracks while the furnace is burning... but I DO NOT recommend homeowners to do this - ONLY PROS...

I would call a pro as the other poster stated.
They will need to use a tester because a mirror to look at the heat X might not do it.
With soot on the chimney cap it could also be a bad check valve in the furnace oil pump allowing raw oil that has not burned into the combustion chamber. That will stink up the house also but the heat X is probably shot.

The heat X for old millers are no longer available so you will need to replace the entire unit. I tried to find one last year and they are NLA.

Thank you both very much for responding so quickly. I will call for a service call and see what they say. The unit is actually 30 yrs old and has been virtually trouble free. So I guess I got my moneys worth out of it!! Thanks again so much! I will let you know what happens. Stephen