L3901 Loader Failure

[AllenBC]

MY L525 loader acted squirrely from time to time in the past, but it would eventually act right. No more. The problem at first was the loader arms were slow lowering and sometimes not lowering but then after a few minutes it would work OK. Slowly it got worse and now the only way to lower is the float function - trying the regular way now actually raises the bucket! Raising the arms the ordinary way now is jerky, but I can eventually raise the bucket. Switching loader arm and bucket quick connects moves the problem to the curl/dump function and the loader works fine. That means the hoses and cylinders are OK and nothing is blocking the quick connects. Hoping a spool valve rebuild would be the solution, I had it looked at by a mobile mechanic and also by a dedicated hydraulics shop. Both removed the spools and found both the spools and everything that can be measured in the monoblock were well within specs. No scratches were found and pressure testing showed no leaks. Their only suggestion is a birth defect: a crack in the monoblock that has gotten worse over the years to the point the valve has totally failed. At this point I am planning to bite the bullet and spend $1080 for a new spool valve unless somebody has a better idea. Anybody even ever hear of such a failure? If cracked monoblocks are known to occur, that will make me feel better about ordering a new one. One final question: Why does Kubota use a two-spool monoblock instead of stacking two single spools?