ZNR Varistor markings

Hi all, (And Tony Duell :^) Have a friends Decstation 5000 power supply with a violently blown fuse. (8A/250V) He is a developer of VMS Freeware (in fact the WASD web server) and has asked me to help. Culprit is 2 x ZNR 14K241U devices, which I believe are Metal Film Varistors Surge Absorbers. The numbering system seems to be obsolete as current ZNR Surge Absorbers use a quite different system, or I've guessed wrong and they are something else entirely, but I don't think so. These two gadgets are wired in series with each other, then connected across the output of the mains rectifier. 240vac in, so they are across around 300+ vdc. I could just leave them out and the supply will run, but would much rather replace them to keep the protection they offer. Their appear to be no other faults and the history of the incident is consistent with a switch on surge after an extended holiday (3 weeks) following daily useage of the machine, so it's possible the reservoir caps may be just a little leaky or the varistor was just getting tired. Anyone make sense of the device id so I can figure out what rating to replace them with. Device looks rather like a round ceramic capacitor, but gloss black in colour, marked with white lettering A Logo consisting of a small square box in top left with a capital M inside and ZNR in caps next to it then under it is 14K241U (or the 1's could be ell or i, hard to say). underneath at bottom left is an reversed italic capital R with a reversed italic capital L joined to the back main bar of the R. To the right of this is a small letter s raised above the baseline with the number 20 after it. Any help appreciated. Cheers Geoff in Oz