I must admit I have no clue on the lens material but I'm guessing glass with it being made in the early 1970's, It seems clean but I will have another look. Other photos have turned out well as long as they don't have the contrast, I will bare this in mind in the future and in low light try to avoid too much sky, Here's one of the good ones on the same day. It seems to have done quite well considering the conditions.
View attachment 179627
There is flare visible in this photo as well - you can see it around the relatively small area of very bright sky near the top.
The sky isn't the problem - it is the big difference between the bright sky and the foreground which is essentially in the shade.
If you were to turn around and take a photo with the sun behind you, you wouldn't see the flare because everything would be more evenly lit. Of course in this circumstance you wouldn't see the train either!
The lens may be dirty, damaged or may just be prone to flare.
One of the features of more expensive high end lenses is that they are designed and coated to minimize flare in situations like this.
Once you know it is there and under what circumstances it appears, you can use flare to your benefit. Think beautiful, soft slightly backlit or sidelit portraits.