Sort of breakdown

["Martin C. Jones" <M.C.Jones@staffs.ac.uk>]

After paying at a petrol station at the weekend, I returned 
to my MGB, turned the key - no response. Indications seemed 
to point to the starter motor. I rocked her to and fro in 
fourth gear, tried again and hey presto she fired up. 

My question is: 

Can this happen as a one off or should I check out the 
starter motor? I seem to be OK with it this week so far.

Regards,

Martin