Help with SL60 starting problem please

Hi, I need some help with a starting problem with an SL60.

Intermittently, about once or twice a month, when the key is turned there is no response at all.

No clicking, no dash lamp dimming, no attempt from the starter motor, just nothing.

Wiggling the gear selector or key doesn’t help and never has.

Sometimes it will go on the next try; sometimes it takes 6 or 8 tries.

The local shop are no help, as it won’t do it when they have it with them.

Any ideas please ????????

Graham