Could you please correct my sentences?

There is a guy who fixes my car. He works in is the only garage that is close to my house and so I go and he fixes my car. He is a nice enough guy. He had seen saw me on a broadcast maybe a year or two after I started going to him and because of that, now whenever I see him, he talks about it on and on.

* If I use "he has seen me" instead of "he had seen me", does the sentence still make sense? or does it sound awkward?

It makes more sense to saw "he saw me" rather than "he has seen me" or "he had seen me" in this instance because you are talking about events that were completed in the past. 

Could you please correct my sentences?

There is a guy who fixes my car. I go to him for car repairs because his garage is the only one close to my house. He is a nice enough guy. He saw me on a broadcast maybe a year or two after I started going to him. Because of that, whenever I see him, he talks about it on and on. 

* If I use "he has seen me" instead of "he had seen me", does the sentence still make sense? or does it sound awkward?

Could you please correct my sentences?

There is a guy who fixes my car. He His [1] is the only garage that is close to my house and so I go and he fixes my car. He is a nice enough guy. He had seen me on a broadcast maybe a year or two after I started going to him and because of that [2] now, whenever I see him, he talks about it on and on [3].

* If I use "he has seen me" instead of "he had seen me", does the sentence still make sense? Or does it sound awkward? [4]

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[1] Your original sentence started, "He is the only garage that is close to my house."  This means that the man is a garage, which of course is wrong.  You have at least three options:

"He works in the only garage that is close to my house."

"His garage is the only one that is close to my house."

"His is the only garage that is close to my house."

[2] Your sentence has a very long run of words without any punctuation, which makes it a little hard to read.  The phrase "because of that" is not needed, so I have suggested removing it.

[3] A more natural phrase would be: "he goes on and on about it".  Your phrasing may in fact be better grammatically, nonetheless to "go on and on about it" is a common phrase.  For example:

"Tom won a medal and now goes on and on about it."

"Please, Tom, don't go on and on about it."

[4] You used the correct phrasing in your composition.  Let's look at two simpler sentences, and presume he saw you in more than one broadcast:

"He had seen me in a number of broadcasts."

"He has seen me in a number of broadcasts."

What's the difference?  The first one is past tense: he saw your broadcasts in the past.  The second one is present perfect tense: he started seeing your broadcasts in the past, and he is still seeing your broadcasts now.

Because you have said that he saw you in one broadcast in the past, 'had' was the correct choice.