Bonjour Carl,
You are absolutely right. All my machines aim to be in hulls where it is very difficult to insert oil in the cylinders with a dedicated pump after a navigation and cast iron rusts very quickly. This is why I was advised to drill the cylinder heads to screw in M3 or M4 caps. With small Viton O'ring seals, they are absolutely watertight and after each navigation, I inject a lot of oil with simply with a syringe. I could possibly have put a pipe on the drain cocks but all my D10 have not them and I have never seen someone suing them fo this purpose.
Example of steam plant in a hull :