Lazy ram when slewing

[steve2371]

Can anyone help.
I have a thwaites alldig over in france on a self build project i'm doing.
It has performed quite well for an old small machine but has recently started to slew very, very slowly to the left but slews fine to the right. If you crack off the hydrolic pipe when switched off it goes back to the left easily.
I am also in needs of new filters for both the oil and fuel. The ones on are crossland filters and I am having problems finding replacements.
the machine is the 3 cylinder perkings engine on.

Any help would be greatly appreciated

Thanks
Steve