Hi,
Great, you found the possible cause.Removing the starter motor is not as difficult as you might think.The top bolt is rather easy,the second one has a shoulder and is going to test your patience and perseverence......
The bottom one is sort of easy as long as you have jacked the car up quite high and using proper support.A long extension with a ratchet,one click at a time,will get it out....
Do not misplace or throw away that spacer!
Once removed,put some fresh plasters on your fingers
Remove the brushes cover and inspect them,Renew them if they are shorter than half an inch.I usually replace the solonoid.
The starter motor on the S2 is very puny,I have removed,serviced and replaced my starter many times.I am saving up,to replace it with a reduction gear starter motor.Whilst you are there in the general area,don't forget to check the oil level of the steering box,I usually mix 25% oil with 75% grease and fill her up.The rubber seal at the bottom is usually hardened allowing the oil to deposit on the garage floor,nothing beats the smell of gearbox oil
Best Regards