Park at the suggested parking area and head north following the Herefordshire Trail along the road that sits on top of the ridge. At Hooper's Oak Cottage leave the road and follow the trail on the right. After a couple of hundred feet or so the trail splits again, keep right and you will find yourself in a real country lane!
At various points along your walk to the cache you will be rewarded with great views through the trees, there is even one just a couple of feet past the cache. GPS accuracy is probably suspect under the trees so you may need to decrypt the hint.
Sadly I have no idea who Mr Hooper was nor why he had an oak named after him, nor exactly where this oak is - if indeed it is still standing. If you know then please feel free to include this information in your "found it" log.