I have a 1986 204C overnigter that I recently purchased. The fuel gauge was working only erratically. Jumping up and down and sometimes not reading at all. I rewired it from tank to gauge and as I filled the tank slowly it appeared to work fine coming up to full as the tank got there. Since then I should have used about 3/8 to ½ a tank but the gauge will not come off the full mark. I have tried tapping on the sending unit (suspecting that it was stuck) with no results. Is the sending unit for this model still available or is there a replacement?