gwanrisire sae yeolsoereul butakhareo gaya hae.

-(으)러 가다/오다 is a purpose clause meaning “to go/come in order to ….”
• 부탁하러 가다 = “go in order to ask a favor.”
You attach -러 (to 하다 verbs you lose the 다 and add 러) and then a movement verb like 가다/오다. This pattern is only for indicating purpose of going/coming.

• 부탁하다 is used for asking someone a personal favor (e.g., “Can you help me?”). It’s more casual and common in daily life.
• 요청하다 is more formal and neutral, often used in official or business contexts (e.g., “Please send the report”).
In your sentence, you’re asking the 관리실 staff a small favor, so 부탁하러 fits better.

Both 새 and 새로운 mean “new,” but:
– 새 is the shorter attributive adjective and more natural in everyday speech before nouns.
– 새로운 is slightly more formal or emphatic and often used in writing or when you want to highlight novelty.
So 새 열쇠 is the usual spoken form.

Yes.
• 가야 해(요) and 가야 돼(요) are interchangeable in most contexts, both meaning “have to go.”
• -해 comes from 하다, -돼 comes from 되다; regional speakers may prefer one over the other, but there’s no major meaning difference.

You can add polite endings and use an honorific request verb:
• Casual polite: 관리실에 새 열쇠를 부탁하러 가야 해요.
• Formal polite: 관리실에 새 열쇠를 부탁하러 가야 합니다.
• Even more honorific (to show extra respect): 관리실에 새 열쇠를 부탁드리러 가야 합니다.
In speech, adding 요 or using -습니다 form makes it polite, and 부탁드리러 raises the politeness of the request itself.