Paul, Have you looked at all of the Service Stamps in your Service Booklet? This should reflect the fact that a Service is due every 10,000 miles (or so ) or Annually, WHICHEVER COMES SOONER.
Consider taking out a Service Plan which you pay monthly by Direct Debit and which helps your cashflow when Servicing is due.
My GS has only covered 62,000 miles but has had its 100,000 service due to age.