How can I fix my Thema classic F30E?

The seal has gone on the diverter valve allowing water to leak into it's mating part rendering both parts knackered.
I have been quoted approx £60 for a new valve plus £135 for it's mating part. With callout and labour and VAT the total bill will be around £350.
The boiler is only 3 years old and I have already spent over £300 on replacing thr pressure release valve (twice ) and having an external pressure vessel fitted.
Is it worth continuing with this boiler? I am fearful that before long something else will go.