Slow Building Oil Pressure - Sudden Onset

[230/8]

Here is the issue:

Background: I have a 1969 230 sedan with the M180 engine. It was rebuilt several years ago and has received only seasonal use since then. It is stored through the winter. When starting it in the spring I would always roll it over a minute until the oil pressure raised the gauge and the carbs filled with gas. Then I would pump the gas a few times and, barrooom, it would start every time, no surprises. I use Mobil 1 15w/50 and have for a long time, there are no leaks and it uses absolutely no oil. In all respects, but one, it is a honey of a motor in a classic model. I've owned it 30+ years.

Problem: Two summers ago, I noticed that the oil gauge would not raise when it cranked over, no matter how long I cranked the starter. I did not want to run down the battery so I patted the gas and, barrooom, it started up fine. And the oil pressure gauge moved off the peg like normal. However, ever since then it has done the same thing with the gauge and also, and this is what troubles me, it has a pronounced but very brief bearing rattle for the split second it takes for the oil pressure to build after it starts. This is happening any time it starts from cold. Once the engine is running there is absolutely no noise from the innards, just the good running it has always had. But that cold start rattle really bugs me.

Could it be a worn oil pump and/or oil pressure relief valve? It happened so suddenly...put it away on the fall, just fine; woke it up in the spring and rattle knock. Scares the pants off me. This is a really sweet engine with no other problems. I am reluctant to say that it needs another rebuild with only 12,000 on this one.

Any thoughts?

Thanks,

JCH, aka 230/8