In my opinion it is slightly worrying that the copper base of the block is attached to the plexi top via threads in the plexi top, as opposed to the thread located in the copper base. As far as I know, plexi does not like to be stressed in this way, especially around drilled parts. There could be a possibility of microcrack formation around the threads, leading to the loss of proper contact between the top and the o-ring and eventual leaking. Plus, if one thread goes bad, it puts extra stress on the remaining threads...