B&K model 747 Dyna Jet solid state tube tester

Hi, I am selling my B&K 747 tube tester, I have had this about 20 years, I am not a tech or radio buff, I bought this for my studio strictly for testing my guitar amp tubes, so it's had an easy life for as long as I have had it. Everything works on this unit and it has the complete tube chart with just a few underlined tube values, otherwise, it's a clean example, (no rips or tears) I have the downloaded copy of the owners manual and one of the tube leads for tubes with a top contact points mounted to the top cover, it's pretty clean outside with the usual scuffs, and two small dents on the corners in the plastic, this was like this when I bought it plastic is not cracked anywhere. It sat on a shelf in the studio for the past 5 years with just occasional use. I used this for a couple nights last month while getting some amps up to spec and found that the grid emission lit up on every tube, this never happened in the past, (it even did it on  2 brand new JJ tubes) so something is wrong with that test, in the manual there is a page that shows how to remove the panel, under the panel it shows, bias adjust, grid emission adjust, shorts adjust and more with two pages on how to calibrate it, I have never done any adjustments in 20 yrs. I have never had the panel off. I  tested more tubes with this the last few days, once its been on for a while and warmed up, it works just as it did in the past, I tested 2 Mesa and 2 JJ tubes that had the values written on the boxes and they tested the same or very close, to what I had written on the box. I see services and kits offered for calibration but I really don't have the time to jump into another project. I am selling this as a working unit, but It may need  calibration. The inside of the unit is clean, all the sockets are in great shape, no damage to any of the slide bars, knobs, or buttons. Serial number ( I hope ) 15-07393. Price is firm no best offer in this listing, if you want a clean, well kept, working B&K this is a good one!