Sorry for old school question.... but read several sources and they say different colors and sizes.

Truck is 2000 LM7 stock 200K mile oil pump.

Pressure has been down a little around 30-35psi last month or two, was always 40-45 until last month or two. So hoping changing O ring will fix it, as it is way easier of a job verse swaping pump for new one.

Hell if I have to swap pump might as well put a larger cam in, but I really don't want to do that or spend the time/money.

 

Have you tried a heavier oil? With 200k I'm betting the clearances are a little looser.

As for the oring...get one of each color. They're cheap enough.

Hell, I've got an extra one I can send along with some water pump gaskets. Free just send me a PM with your address.

If you do a cam...now is a good time to replace the pump and do a new timing chain with the newer dampers.

I would highly suggest having the proper tools. I've been stockpiling tools for the last few months. I got a very good pulley puller that I got to use Friday and I'll tell you what, it made getting that crank pulley off a breeze.

I also have the pulley install tool as well. You can also use a ls7 crank bolt to get the pulley back on.

Get 2 5/16 wooden dowel rods to hold the lifters up. Cut them to 22in.

 

If using an OEM or Melling o-ring just decipher the chart.