Yep, I've had that happen about 3 years ago so I'm fairly sure it's the starter.
1st check all the cables are clean, bright, and tight, if they are and the problem still exists you can replace the starter or try to bring the current one back to life.
Here is how I brought my starter back to life.
Removed the starter from the engine, removed the 2 through bolts and the starter comes apart.
Cleaned out all the carbon and removed all loose rust, taking time to remove all the rust stuck to the magnets in the black starter housing.
Cleaned the tarnishing from the copper area where the brushes contact the armature with scotchbrite.
Checked the brushes are at least 6 mm thick and free to travel on the springs.
Cleaned everything again.
Made a tool to hold the brushes in place during re-assembly, this is nothing more than the lid of a CD case (or similar thin but stiff material) with a slot cut into it to allow to to slide it out when everything is almost in its place.
Examined the alignment markings on the on the stator and the end caps to make sure the stator goes back on the correct way up (otherwise it will run backwards and do nothing)
Holding the brushes down with the tool, put the 3 pieces back together, slide out the tool.
Dropped the through bolts in and tightened them up.
Re-installed on engine and never been a problem since, in fact I'm sure the motor turns over faster than ever before and has improved the starting.
Time from start to finish 30-40 mins* cost 0.
You could try it.
How did you know someone called Dave would answer?
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