Is this plagiarism?

I think the copy rights are over after a period of time. Also, the teaching is fundamentally old school doctrine taught by pretty much all true bible believers. If anything Doc preserved historical teachings that I'm glad haven't slipped away. I don't fault him. Some things are better left to the Lord Jesus Christ to decide. I wonder what the Lord thinks about plagiarism? I know what he thinks those who sow discord among the brethren: Proverbs 6:16 These six things doth the LORD hate: yea, seven are an abomination unto him: 17 A proud look, a lying tongue, and hands that shed innocent blood, 18 An heart that deviseth wicked imaginations, feet that be swift in running to mischief, 19 A false witness that speaketh lies, and he that soweth discord among brethren.

This is a big waste of time, but the book for the Theological studies, are actually transcribed from the radio program. Maybe Doc was reading from the book that you accuse him of plagiarizing from...

Plagiarism and copyright laws are not synonymous. Plagiarism is the act of presenting another's work, thoughts, and/or ideas as one's own. Now, simple or common phrases, though unoriginal with subsequent authors, may be used without attribution. For instance, no one demands a footnote for saying "kick the bucket." Closer to home topically, no one would object to saying "The Trinity is defined as one God manifest in three persons," though that sentence, in that order, likely appears in multiple works throughout time. However, it is evident from the examples that he copied, in many cases word-for-word, the source material. Since it is highly implausible that Ruckman was writing independently and the phrases are not common, especially in sequence, Ruckman presented work not done by him as his own (incidentally qualifying for the "lying tongue" bit above). Also, positing a similar but different source from which both works may draw is just irrelevant. Since the old work predates Ruckman, we know the older author cannot be copying from Ruckman. It follows, regardless of whom he is copying, he is indeed copying. Finally, appealing to the results to justify plagiarism (or quotes without attribution [not that he used quotations]) is misguided as well. He could have achieved the end you describe (preserving theological history) even more efficiently by providing adequate attribution. He committed plagiarism, plain and simple. Were any indication given that he merely forgot to add attribution, it'd be one thing. But he clearly took pains long enough to add a couple of the words here and there, meaning he intended the use of the text as a near-identical quote (some entire consecutive sentences being mirrored) but didn't footnote any of the ideas therein. In academic writing, plagiarism is not only lying, it's stealing.

Plagiarism? Of course...almost word for word. As a matter of fact, if that were presented as a finished, personal work in ANY worthwhile, accredited school, he would have been hauled in the Profs office for an explanation at the very least...expelled at the very worst. The proof is in the pudding...to come to any other conclusion would be just as dishonest as commiting the act yourself.

It is as clear a case of intellectual theft as I have seen

Yes. It is even not cited. And there is the same word order.