Woody's water heater overflowing.

Hi, came on here since I saw that people were familiar with these. Basically, overflow keeps dripping. Obviously suspected the t and p valve.On inspection, various o rings, nitrile and rubber, had failed. Went to simply replace but no joy here in Spain or Europe it seems as 2 port version (1 for main tank 1 direct into draw off coil). So, put ordinary pressure release valve in the line before the Woody's valve but no difference so I suspect that the actual high pressure valve itself is not sealing properly.It doesn't look like u can replace just that lever seal. So, even if I get a new one from Australia, it's 200 bucks plus postage and tax where they will mug us here. So, can I not just find / cobble together an arrangement where I have the new 10 bucks pressure valve in the line direct to plumbing which simply feeds the 2 ports? Bear in mind, the tank seems designed to have air at the top just above the overflow outlet so, other than the spring valve on the inward end if the pressure release valve, there is no restrictiin in water simply flowing through. I.e the pump fills, the overflow allows it out, the pressure reduces so the pump fills. All suggestions welcome. Nb a whole new set up would be about 2k Aussie dollars! If anyone can even explain how it is supposed to work i.e. what is supposed to stop the intake of water if the overflow is constantly open, how can the tank produce any pressure for any intake valve to stop supply -- bearing in mind the schematic shows it can be used for mains supply which. is faar higher pressure than boat pump?

My understanding is that the woody's water heater is an unpressurised cylinder fitted with an element and two coils within it, one connected to the engine cooling, the heating coil, and the other connected to the domestic water supply, which heats the water as required. The domestic water flows through the coil and thence through the pressure relief valve which releases into the cylinder, the manual release being used to fill the cylinder. when full or pressure releasing the cylinder overflows to the bilge, or wherever it is directed.
My experience has been that it is a very effective water heater with the only consumable being the pressure relief valve. Unfortunately I cannot offer any alternate suggestion other than attempting a rebuild or possible alternate install.
Good luck.

For those that were interested and for future knowledge, I have figured out the problem. The heater is unusual in that it works like a heat exchanger: the elements heat up the tank but it is not that water that is drawn off - the cold feed runs through the draw off coil, the water inside it gets heated by the surrounding tank water, and then goes to the taps. The problem I found is the the draw off coil is leaking into the main tank which then overflows. No way of changing the coil and given that it is 20 years old, probably best to buy a new tanks and replace everything. (I did contemplate turning it into a more conventional system but a lot of work on an old thing!) That said, there will soon be a nice stainless and copper tank by the bins in Almerimar!