يتفقد المشتري الدواسة وذراع المكابح وعمود المقعد ومبدل السرعات.

Because a very common neutral word order in Modern Standard Arabic is verb + subject + object.

So:

• يتفقد المشتري... = literally inspects the buyer..., but naturally the buyer inspects...

This is normal Arabic word order. You can also say:

• المشتري يتفقد...

That is also correct, but it is more subject-first and can sound a bit more topical or emphatic.

يتفقد is a present/imperfect-tense verb meaning he inspects / checks / examines.

More specifically:

• past tense: تفقّد
• present/imperfect: يتفقد
• person/gender/number: 3rd person masculine singular

So by itself, يتفقد means he checks/inspects.

Because Arabic verbs already include the subject information.

So يتفقد already tells you:

• he
• is checking / checks

The noun المشتري is then added to state who that he is:

• يتفقد المشتري = the buyer inspects

Arabic often does this: the verb carries a built-in subject, and then the explicit noun follows.

It agrees with the subject, not with the objects.

Here the subject is:

• المشتري = the buyer

Since المشتري is singular masculine, the verb is also singular masculine:

• يتفقد

The list of things being checked does not change the verb form.

In Arabic, و meaning and is written as a prefix, attached directly to the next word.

So:

• وذراع = and a/the lever
• وعمود = and a/the column/post
• ومبدل = and a/the changer/shifter

Also, Arabic very often repeats و before each item in a list. So a sequence like:

• A and B and C and D

is completely natural in Arabic.

Because they are part of an idāfa construction, also called a construct phrase.

In an idāfa:

• the first noun usually does not take الـ
• the second noun defines or specifies it

So:

• ذراع المكابح = the brake lever
• عمود المقعد = the seat post
• مبدل السرعات = the gear shifter

Even though ذراع does not have الـ, the whole phrase can still be definite because the second noun is definite.

Yes.

Each one is a two-part noun phrase:

• ذراع المكابح = literally lever/arm of the brakes
• عمود المقعد = literally column/post of the seat
• مبدل السرعات = literally changer of the speeds/gears

This is a very common Arabic structure. English often prefers compact compounds like brake lever or seat post, but Arabic often uses idāfa instead.

Grammatically:

• المشتري is the subject, so it is nominative
• the things being inspected are direct objects, so they are accusative
• in each idāfa, the second noun is genitive

So the structure is:

• subject: المشتري
• direct objects: الدواسة, ذراع, عمود, مبدل
• second terms of idāfa: المكابح, المقعد, السرعات

In normal Arabic writing, the short case endings are usually not written, so learners often do not see these differences on the page.

Because المشتري is simply the noun buyer/purchaser, and this noun naturally ends in a long -ī sound.

It comes from the verb اشترى = to buy.

So:

• المشتري = the buyer

This is normal for this word. Even though it is the subject here, everyday Arabic spelling usually does not show the final short case vowel clearly, so the written form stays المشتري.

Because of sun letters and moon letters.

When الـ comes before a sun letter, the l sound is assimilated. For example:

• الدواسة is pronounced roughly ad-dawwāsa
• السرعات is pronounced roughly as-surʿāt

When الـ comes before a moon letter, the l is pronounced:

• المشتري = al-mushtarī
• المكابح = al-makābiḥ
• المقعد = al-maqʿad

So the spelling stays the same, but the pronunciation changes depending on the next letter.

Yes, absolutely.

Both are correct:

• يتفقد المشتري الدواسة...
• المشتري يتفقد الدواسة...

The first is the more typical verb-first pattern in MSA.
The second is a subject-first pattern, which can feel a bit more like As for the buyer, he checks... or simply put more focus on the buyer.