2007 Bobcat zhs 435 swing break relief valve assy. P/N 6678788

I have a leaky rotator (slew) brake relief valve assy that rusted thru . It still works but leaks constantly under pressure . iT IS PART NUMBER 6678788. or an alternate if anybody knows of one . This is a great little 435 , it's has been strong and dependable , especially in a harsh environment of sand , salt ,volcanic ash , tephra , sulfur , rain etc . Keeping it inside or covered is paramount , that why this rusted thru . If you have any info please let me know .