Malc,
can't comment on the 200 psi reliability as it's in my back up machine and doesent run much, but it will be the same design as my 400 psi Ninja wich is very reliable and has run for 18 months without attention.
I have just stripped the pump head on the 400 psi and all is well. Cleaned, checked for wear and regreased the piston etc, very easy to do.
I have found the 400 psi to be much more reliable and robust than the 135 diaphragm pumps.
Ashbys will convert to the 400 psi for around £500. Better done by Ashbys as it can be quite involved.
I did the 200psi conversion myself, took about a day....much more work than it looks, fitting extra elbows and connectors etc and it says on the instructions, fitted in one hour

John