Though the Qur’an has not been altered, it is written in a dialect some 200 years older than the time of Mohammed and was therefore not fully understood even by his contemporaries.
You are correct when you say that the Qur'an is unaltered, but the rest of your point is not
true at all. The Qur'an itself contradicts what you have said, by affirming many times that it is in plain Arabic, easy to understand and explained in detail:
So We have made this (the Qur'ân) easy in your own tongue (O Muhammad ), only that you may give glad tidings to the Muttaqûn (pious and righteous persons - See V.2:2), and warn with it the Ludda (most quarrelsome) people. [19:97]
Verily, We have sent it down as an Arabic Qur'ân in order that you may understand.[12:2]
And indeed We know that they (polytheists and pagans) say: "It is only a human being who teaches him (Muhammad )." The tongue of the man they refer to is foreign, while this (the Qur'ân) is a clear Arabic tongue. [16:103]
Muhammad (peace be upon him) explained the Qur'an to his companions, who thus had a very strong understanding of it and this is why we must refer back to their understanding to interpret it correctly. Their insight into its meanings would be quite apparent if one was to actually study the science of the Qur'an - specifically, the manner in which it is interpreted. Furthermore, the clarity of the Qur'an and recognition of this by people at the time of its revelation is clearly demonstrated in the accounts of the pagan Arabs who were moved by its recitation - some of whom even became Muslims simply through hearing its divine message!
Words also have the habit of changing their meaning over the centuries, not to mention being altered in meaning by translation.
Since you already (correctly) mentioned that the Qur'an is unaltered, then evidently this habit of words to keep changing does not apply to the Qur'an. Also, a translation of the Qur'an is not considered to be the Qur'an, and although we accept that translations cannot completely convey every meaning in the Qur'an despite the scrupulous efforts of translators to preserve the meaning as much as possible, this does not mean that the original Qur'an has become changed; the Arabic has remained intact.
Even more of a headache for Islamic scholars than the interpretation of the Qur’an is the authenticity of the Hadith, which were not even transcribed by Mohammed.
Well obviously they could not be transcribed by Muhammad (peace be upon him) himself as he was an illiterate man, which is why it is all the more a miracle that he came with the Qur'an. The companions of the Prophet (peace be upon him) wrote down the hadeeth and they were also preserved in memory. The hadeeth have been preserved so meticulously that there is a whole science in Islam with respect to their study. You can read more about their preservation here:
You may also be interested to have a browse through: http://www.islamicboard.com/islamic-...ct-hadith.html
The question therefore should not be whether or not Islam has degenerated - for what purpose would serve the Mahdi - but in what way has it degenerated?
Islam itself does not degenerate, it is the people who claim to follow it that do. The Mahdi will bring back peace and justice, but that does not mean he will be laying down a new religion altogether, as the only religion in the Sight of Allaah is Islam.
There is no mention of stoning as a punishment in the Qur’an.
No, but it is mentioned in the hadeeth. Read more here: http://www.islamicboard.com/islamic-...g-death-3.html
and any conviction requires 4 witnesses of unblemished character.
No, not "any conviction". This is in the case of illegal intercourse.
A person with enough money to pay off the family of his murdered victim, in many instances would walk free under Shariah law.
No, that is not correct - the victim's next of kin have the choice of whether or not to accept the blood money as compensation.
Can the Hadiths that advocate stoning be accepted as authentic when they go against the spirit of the Qur'an?
They don't go against the "spirit of the Qur'an" at all. The reason for your misunderstanding is because you do not fully understand the concept of the hadeeth. Both the Qur'an and the hadeeth are sources of Islam; not just the Qur'an. This has been explained many times on this forum, and you can read more about it in the following threads:
The explanation that the passage in the Qur’an that outlined such punishments was eaten by a goat seems rather lame to modern eyes.
It's not lame; it's false altogether.
[6:115] The word of your Lord is complete, in truth and justice. Nothing shall abrogate His words. He is the Hearer, the Omniscient.
The Hadith does indeed 'abrogate His words'.
Let us look at a proper translation of the verse, which is, according to the Muhsin-Khan translation:
And the Word of your Lord has been fulfilled in truth and in justice. None can change His Words. And He is the AllHearer, the AllKnower.[6:115]
So first of all, this verse does not explicitly mention abrogation. Abrogation did
occur with the Qur'an, and it was also possible for hadeeth to abrogate Qur'anic verses. However, not ever single hadeeth abrogated something.
The Hadith often does not explain the Qur'an but provides stories and injunctions in adition to it.
On the contrary, they do
explain the Qur'an, as well as providing additional information. Perhaps by looking at the links I gave you and reading a bit more on the topic, you might learn why.