Plumbing/Main Line Issue (cont.)?

Okay, I've been pondering this problem for 2 weeks now and think I have enough of it nailed down to go ahead and ask someone who has more experience with plumbing. I am no plumber but I am an avid DIYer and eager to learn anything I can. I asked a question similar to this earlier but now I have more information. Here goes: I bought a house a few months ago but didn't move in until about 3 weeks ago. It was built in the late 1940s and has been renovated for the most part. It is single story and has a crawlspace. The house is downhill from the street about a hundred feet away and is on the sewer system. In the main line there are two cleanouts in between the house and the street. One cleanout is right next to the house and the other is right next to the street. Everything was great until about two weeks ago when all of the sudden the toilet would not flush. When you tried to flush it the water would just build up almost to the rim and then gradually it would go back to the normal level (takes 5-10 min). At the same time as this was happening we began to hear gurgling in the kitchen sink. No water or sewage came out of any other fixtures. When running water in the other fixtures (shower, sinks, etc.) there were no drainage problems but lots of gurgling noises. When I opened the cleanout right next to the house (it has a threaded PVC cap), the water was backed up and sewage began to leak out. However, the cleanout next to the road did not have any sewage coming out of it and was not backed up. I took this to mean that there was a clog in between these two cleanouts and I called a plumber. The plumber snaked the main line from the cleanout next to the house all the way to the road. He said that there was a root right at the end of the line and this fixed it. This seemed to fix the problem completely (or so I thought). Now about a week and a half later, the exact same problem has occurred. The toilet won't flush, gurgling noises, other fixtures drain fine (maybe a little slow). The weird thing is that sometimes the toilet will flush fine and no gurgling noises; it worked fine for a week and a half. In addition, I noticed that the top of the cleanout next to the road is broken. The threaded cap is broken off and the pvc around the cap is cracked. Why would the toilet work fine sometimes? Why do we only here the gurgling noises sometimes? I don't want to call another plumber and have them do the same thing. Please try to diagnose. Any help appreciated!