Learn Russian: Каждый аттракцион должен быть осмотрен ежедневно.

The word ежедневно (daily) implies a repeated action, so why is осмотрен formed from the perfective verb осмотреть rather than an imperfective one?

This is a major quirk of the Russian passive voice! Short Past Passive Participles are almost always formed from perfective verbs, even when describing a routine or repeated action. The sense of repetition is carried entirely by the adverb (ежедневно). The perfective participle is used because it focuses on the completed result of the inspection that must be achieved each day.

Why are both должен and осмотрен in their masculine singular forms?

In this construction, both the modal word (должен) and the Short Past Passive Participle (осмотрен) act as the predicate of the sentence. Therefore, they both must agree in gender and number with the subject they describe, which is аттракцион (a masculine singular noun).

Could I use the full-form participle осмотренный here instead of осмотрен?

No, you must use the short form. When a participle is used as the main verb/predicate of a passive sentence (following быть), it always takes the short form. The full form осмотренный is only used when acting like an adjective directly modifying a noun, as in осмотренный аттракцион (the inspected ride).

Does аттракцион mean the exact same thing as the English word "attraction"?