Hi Billy, be very careful adding a stop leak product to any refrigerant system.  When these items come in contact with atmospheric products they form temporary seals.  However, if you have air in your system many technicians believe stop leak products will react forming small clumps that circulate with the refrigerant contaminating and ultimately harming the working components of the system.  Under a warranty claim if Danfoss Compressors determines stop leak has been used in their system it voids their warranty, see attached statement from Danfoss.

I am familiar with both Penguin and Coastal Climate Control and I think both are very reputable companies.  However, I am not sure Penguin will ship Climma or Frigoboat products to the US since Coastal Climate is the authorized US distributor.

As far as your reversing valve is concerned these can be replaced in the field.  It is necessary to wrap the valve with wet rags, old-school, or apply an intumescent coating to the valve to protect the internal components during installation.  If you do this the system must be charged with nitrogen at very low pressure to prevent the formation of carbon on the internal surfaces of the components during heating.  Failure to do so could allow carbon formation which will ultimately slough off and circulate bits in the system creating problems.  I do not believe Climma manufactures their own reversing valve.  With a little research I believe you should be able to find an off-the-shelf replacement.