Have a look at Big Blue Ocean marine, they have Westerbake (Sherwood ) replacement pumps at a discount price.
Just a thought.

Tom,
Sorry for your troubles.Call DEPCO in Clearwater (Tampa)  and ask if they will repair a Sherwood pump and what the cost would be. It's worth a phone call.  They are on the web at  http://www.depcopump.com/    Many times it takes a few more parts to fully rebuild these pumps - more than just installing new seals and a new impeller. Water could be leaking as a result of a scored pump shaft.  I had that problem years ago with my Sherwood and went immediately to the Oberdorfer pump on my M-35. It has worked fine here in Florida for many years. There are many posts here on this site regarding the installation of the Oberdorfer pump. If you do decide on the Oberdorfer, check around for prices at Depco -  Cardinal Pump in St. Louis and similar suppliers. Also, the Oberdorfer sells an installation kit (different part number)  that contains new mounting ears and new elbows for fitting the pump to the engine. (Check my earlier posts for the part numbers or ask DEPCO) It will take you less than an hour to install a new Oberdorfer if you get the kit.
Good Luck,
Bill 
PS; Read post #11 of this article; https://www.catalina36.org/forum/technical-discussion/update-oberdorfer-...

I replaced my sherwood with OBERDORFER with no problem. The correct one is N202M-16 
visit my signature website for images of how to install and how to replace the seals and impeller. 

Tom;
In the 'For what it's worth colum .
Great that you found the Big Blue Ocean price. But to answer you concern; We've used the Oberdorfer here in Florida where the water temperature can reach 92 F in summer and see no problems with the engine cooling. Engine cooling can be effected by several things. Your thermostat 160 or 190 F ? Your heat exchanger 2" or 3". Here in Florida we have a three inch exchanger and a 190F thermostat. Our summer water temperature reaches 92 F. and we have no problems with the Oberdorfer.
We are using the Oberdorfer N202-908 with the round base. (No grinding required and direct replacement for the Sherwood)
The Oberdorfer model N202M-16 you will have to grind off some of the bronze bottom lip of the pump housing to get it to fit on to the M35B engine as Joel did
The Oberdorfer model N202M-837  is a kit that contains the N202-908 pump.(Round base) Two new pipe  elbows (as the ones you currently are using -will have to be cut (shortened) to fit it to the pump)
two brass mounting clamps or ears to hold the pump too the engine, two high tensile strength bolts for fitting the assembly to the engine and a gasket.
Depending on how you approach this, using the kit model will take you less than an hour to install.

Hints;
Use new hose clamps.
Label the water pump intake and out put hoses so as not to mix them up when you put it back together.
Turn the engine  inlet water sea cock OFF to avoid draining too much water out of the system.
Squirt some dish washer soap into the pump  to avoid a dry start on the impeller.
I never found it necessary to burp the water system as the amount of water lost is very small.
 Make sure the water inlet sea cock is turned back ON and that you are pumping water after the start. 

You can always PM me is you run into difficulty.
Good Luck and keep us posted
Bill
PS: Yea that actually a M-35 engine. They repainted repainted it in Universal gold when they rebuilt it. Grrr !
You want to check out the Big Blue Ocean Marine # JPR-WB7108 pump. Although, have no experience with that pump., It looks like that might fit the bill as well. 

My question is, on the original Universals (e.g., M-35) or the Westerbeke/Universal "A" engines (e.g., M-35A) with the pump land on the starboard side of the gear cover ("non B" engines) why would anyone replace a Sherwood with an EXPENSIVE Oberdorfer M-908?  The less expensive Oberdorfer N202M-16 is the pump to install to replace the Sherwood G903 or G908 or M5 or any other one.  I've done a ton of pump switches over 25 years and include stainless steel studs to permanently install and nylock flange nuts (pictured,) rather than bolts into the crappy Kubota aluminum gear cover.

No 3 or 4-cylinder engine owner has ever reported an issue with water flow/engine temperature using the Oberdorfer M-16 pump. 

BTW, the Kubota gasket for that pump land is better than the Westerbeke gasket and the one I always recommend (pictured.)

BTW also the new expensive hose elbows that are supplied in a kit are nothing more than PEX elbows and are brass (which are not approved for below water line and especially not for salt.)  There is no reason to replace them, the Sherwood's elbows very easily fit with 2 minutes and a Dremel or file (the ones pictured are from an M-25XPB) which BTW are also cast brass and not approved.

Ken, I was think of installing studs just the way you have done. Did you use blue Loctite on the studs? They are aluminum studs or stainless steel screw rods?
 

I do recommend a thread locker.  Clean the threads well w/ a solvent/swap to remove any oil; dry fit them; use loctite; tighten down by double nutting or w/ a needle nose locking plier.

They are custom ordered stainless steel studs from the UK,  What's needed is double-threaded studs, unequal length.  I believe what I have for overall length is like 28mm to use for only the flat mount Ob pump, or 32mm if one wants to be able to use the Sherwood L-clips -- if one keeps the old Swood for an emergency or is using the round base pump.