Here the Greek translator has overstepped his own abilities.
There is no error in the original autographs.
This has no evidence. I am just as willing to say that it was the author of Matthew, writing in Greek, who didn't realise what was going on. I have little doubt that he was not an eyewitness to the event. When he wrote the gospel, he used the confessional understanding of the First Testament that he recognized, but at times mis interpreted it.
Isn't it also fascinating that the first corrector of Sinaiticus omits the επι πωλον in the fourth line of the quotation from Zecheriah, but not the repitition from verse seven? Isn't it also fascinating how explicitly the LXX of Zech. 9.9 reads:
και σωζων αυτος πραυς και επιβεβηκως επι υποζυγιον και πωλον νεον.
It doesn't sound so Hebrew any longer.
You don't need a 'Q' source, only a fool of a Took trying to render Hebrew into Pidgeon Greek.
These kinds of statements are scary.
An obvious complete failure to recognize the standard form of Hebrew poetry, repetition with synonymous construction. And please don't tell me there were two animals, instead of one ass translating, unfamiliar with the correct version of the story correctly translated in Luke. You don't need a 'Q' source, only a fool of a Took trying to render Hebrew into Pidgeon Greek.
So now to the meat and potatos. You have provided here a fun opportunity for redaction criticism:
bold = verbal parallels Mark/Matthew
Underline = verbal parallels Mark/Luke
<> = verbal parallels Luke/Matthew
italics = significant nonverbal parallels
NB: where there was simple reversal of word order I still considered it a verbal parallel.
_Mark 11:1-3_
αποστελλει
δυο των μαθητων αυτου και λεγει αυτοις
υπαγετε εις την κωμην την κατεναντι υμων, και ευθυς ειςπορευομενοι εις αυτην ευρησετε πωλον δεδεμενον εφ' ον ουδεις ουπω
ανθρωποων εκαθισεν λυσατε
αυτον και φερετε.
και εαν τις υμιν ειπη τι ποιετε τουτο ειπατε
ο κυριος αυτου χρειαν εχει, και ευθυς αυτον αποστελλει παλιν ωδε
_Luke 19:29-31_
<απεστειλεν>
δυο των μαθητων <λεγων>
υπαγετε εις την κατεναντι κωμην, εν η
εισπορευομενοι ευρησετε πωλον δεδεμενον,
εφ' ον ουδεις ποποτε
ανθρωπων εκαθισεν, και <λυσαντες>
αυτον αγαγετε.
και εαν τις υμας ερωτα δια τι λυετε ουτως ερειτε οτι
ο κυριος αυτου χρειαν εχει.
_Matthew 21:1-3_
Ιησους <απεστειλεν> δυο μαθητας <λεγων> αυτοις πορευεσθε
εις την κωμην την κατεναντι υμων, και ευθεως ευρησετε ονον δεδεμενην και πωλον μετ' αυτης <λυσαντες> αγαγετε μοι.
και εαν τις υμιν ειπη τι, ερειτε οτι
ο κυριος αυτων
Χρειαν εχει.
ευθυς δε αποστελει αυτους.
Notes:
It has long since been recognized that a significant feature of Markan style is the rather ugly usage of the adverb ευθεως. It hardly needs to be said that its use in some 40 different verses in that gospel is not to be considered good Greek style. It is used in almost part of the parable of the seeds of chapter four. In contrast, Matthew uses the term in only 15 verses (and his gospel is significantly longer, too). Of those, a number are stories which show marked parallels with a Markan version: Mt. 4.22/Mark 1.20; Mt. 13.5/Mark 4.5; Mt. 4.22/Mark 6:45; Matthew 14.27/Mark 6.50; Matt. 20:34/Mark 10:52 (despite the classic numerical discrepency, it's obviously the same story); Mt. 26.49/Mark 14.45. These six account for over 1/3 of the uses of ευθεως in Matthew, and in a number of circumstances it is employed in an obviously-Markan idiom. Add to that the fact that Mark and Matthew share the clause of returning the animal(s) and you have a very interesting case.
This is especially so when you notice that Luke omits both instances of ευθεως and the clause about returning the animals. Luke is almost entirely the same as Mark except for these changes and a couple of grammatical cleanups: απεστειλεν and λυσαντες, both of which used by Matthew as well. Another difference which makes the whole thing flow better in Greek is the phrase δια τι λυετε rather than the colloquial τι ποιετε τουτο. Matthew's is simplified into, "if anyone questions you."
What I am suggesting in all of this is that you have a strong reason for seeing an independent use of Mark by both Matthew and Luke. It is less likely (though not impossible) that Matthew was the impetus of Mark. However, it makes the timing difficult because Mark would have to have been completed and dispersed so that Luke could use it; it also goes against common sense as the reason for the ευθεως, since this is a Markan feature; and also because it would be odd for Mark to denigrate the grammar of Matthew.
These brief notes also have a bearing on the Hebrew-original theory. The parallels here are in Greek, not in Hebrew. You suggest that the translator of Matthew was poor, but in fact he renders many phrases in fine Greek. It is difficult to imagine him making a 'mistake' like you've mentioned. Rather, it is more likely that it's not a mistake at all, but a reading of the LXX-tradition plus a Matthean fettish for pairs in everything.
Oh come on. There's plenty of material from the first and second century which is fully in line with modern orthodoxy and which might happily be included in our bibles. Why not just add a book or two? Heck, why not add something entirely pseudepigraphal? If there's no problem with someone inserting it into a document though not written by the writer of that document, so long as it agrees with your own theology, then
why would an entire b ook be any different.