On the topic of Pansonic service discs, I did some corresponding with the Panasonic Parts department, and the service disc for the DVD-RP91 is part number DVDT-S15A -- and goes for $100!!!
I found a second source for the disc, www.vancebaldwin.com,
and they have service discs for a number of players:
Players: dmre20d, dmre30, dmrhs2
Players: pvd200, pvdv200, pvdv200d, pvdv400, pvdv400d, pvdv51, pvdv600, pvdv800
Players: dvdcp72, dvdlv65, dvdlx9, dvdrp62, dvdrv31u, dvdrv32, dvds35, dvdxp30, dvdxp50, sadk10, sadp1, saht690, saht70, saht700, saht900, sast1
Players: dvdlx9, dvdrp91d
Disk #DVDT-S15 (no longer available; substitute disk #DVD-S15A for this disk)
Players: dvda100u, dvda105u, dvda110u, dvda115u, dvda120u, dvda300u, dvda310u, dvdc220d, dvdcv50u, dvdh1000d, dvdk510d, dvdk520d, dvdl10d, dvdl50d, dvdla95pp, dvdlv75d, dvdlx9, dvdp10d, dvdpv55d, dvdrp91d, dvdrv31u, dvdrv80u, dvdt2000, sast1
Players: dvdlx9, dvds35, sast1
Note that the RP91 service disk at Vance Baldwin is $45 more than panasonic quoted me directly.
Panasonic orders can be placed at www.pasc.panasonic.com
(20% off shipping), or at (800) 833-9626 or (253) 395-7343.
I'd really be interested in getting my hands on the RP91 disk -- but can't justify spending $100 on it at this time.