KLE 500 : No oil pressure suddenly

I recently replaced the rotor on the KLE. In doing so I had to drain the oil and remove the sump so I could clean the oil pump sieve. Remember the bike was running perfectly prior to me replacing the rotor. I only discovered the delaminated magnets on the rotor because I was replacing the brushes on the starter motor and had to take off the rotor cover.

I fitted the new rotor and reconditioned starter motor, re-installed the sump plate and checked all the seals where in place, filled with oil and started the bike. The bike started perfectly and idled for about 5 minutes but the oil light did not want to go off. I checked the electrics and tested the oil pressure switch with a bit of compressed air and it does work. I just can understand what suddenly has gone wrong. Can it be the seals on the sump plate that are not sealing properly? What is worse is that if it is suddenly a oil pressure problem then would I have damaged the bearings on the engine in the 4 to 5 minutes it was idling while waiting for the oil light to go off? In the meantime I have ordered new sump seals and a oil pressure switch and will just change it as a matter of course to eliminate it. This is a total mind fark as I can't understand why I suddenly dont have oil pressure. Any advice would be appreciated. Perhaps someone has had a similar problem on a KLE.