Yes, you can do it yourself as long as you're willing to buy a Service Manual (usually available on line for about $10), any tools you don't already have, including a torque wrench, have the time, determination, desire and patience to see the job through.I really appreciate the extensive help. I really wanted to hide my head in the sand and think "bad head gaskets can't happen to me." As I said, I'm not a mechanic, so the only way I knew to test/check was to remove the head. So thank you very much @pyromedic for suggesting various tests. I did order a replacement cap. But I also went to Harbor Freight and got a Combustion leak test kit. And...
Yellow! Even worse than I thought. Can I do a head-gasket replacement myself? I have a good bit of patience and can follow instructions.
Several times in previous posts I've stated that I learned early on that spending money on tools and learning to fix my own stuff has paid off many times over. I still have and use the tools I purchased when I was in my late teens and have continues to add to them over time. They have paid for themselves in saving me money at repair shops, insuring the job was done right the first time and providing me with a good education on mechanics.