It's not likely that upgrading the firmware will help. Although firmware could conceivably affect the laser by varying the power, and thus the reading/writing capability, unfortunately the signs in your unit are typical of a machine with a gradually failing laser. The incapability of reading commercial pressed DVDs is a late effect and has a bad prognosis. Replacement of the optical part of the drive is the only reliable solution.
Philips did offer an extended 2-year guarantee to some machines, notably a proportion of the 8x0 series which were fitted with faulty optical pickup units, but your 985 would probably be too old to qualify.
Still, they can only say no. Why not try the method linked above and see what happens.
Otherwise I would say it's not economically sound to repair. There's a really wide choice of new DVDRs now, many of which will still play the +Rs you already have.
It would be nice if the original contributor got back with some progress, if any.