Just to add to Jane's answer: 'Tar the cracks' sounds like an old nautical idiom. If a wooden boat or ship has cracks in its structure, filling them in with tar will stop leaks occurring - at least for a while. It seems to suggest finding a temporary solution to a problem. It's similar to a more common idiom to 'paper over the cracks' (hiding cracks in a wall with wallpaper rather than fixing them). I have never heard the idiom about tarring cracks, but it seems to make sense. I wouldn't be surprised to hear someone use it.

A nitwit is a person who has done something foolish - I often tell my son he is a nitwit for spending all his money so quickly. The infirmary is a word we use to talk about the hospital - I have an appointment at the infirmary. It is very common in the area of England that I am from, the North, however, it may not be popular in every area. That place will have got the best of me - or - that place will have had the best of me. When I retired from working in a university I said that place has had the best of me - meaning I gave them my best work, knowledge and skills while I was there. A sweepstake is gambling and is often used for people who gamble on horse racing. The sweepstake winner accepted his prize after the race. Some people (have) really got it bad (not awful) - This can be used in a few ways depending on what you are trying to say. e.g. Many people are catching flu at this time of year and some people have got it really bad e.g. she has got it really bad for the new guy at work - meaning she really likes the new guy I'm not quite sure what you mean with the last sentence but I hope the two examples make sense.