How does this conversation in Shadows of the Empire make sense?

I actually liked Steve Perry’s Star Wars novel Shadows of the Empire from 1996, but there are a couple of things that keep my head spinning. Above everything else, I don’t understand the following conversation, which takes place in chapter 37 when Luke, Lando, Chewie and Dash run into Leia in their attempt to rescue her from Xizor’s castle (the given page references hold true for my softcover version of the book):

"Took you long enough," she said. She looked closer at them, wrinkled her nose. "Gah, what have you been swimming in? You smell like that stuff Lando tried to feed us. And you look like it, too."

"The ship broke down," Luke said. "So we had to take a shortcut through the sewer."

Both of them glanced at Lando.

"It was not my fault about the ship," Lando said. "It was Han’s modification!"

First of all, Leia saying that it took them "long enough" is irritating because she could not have known that the guys were coming for her in the first place. They hadn’t agreed upon that plan with Leia beforehand – on the contrary: Leia even told Lando in advance that she could take care of herself (ch. 27, p. 255). In fact, it was only through a Force ripple that Luke realized Leia was in danger (ch. 29, p. 274) and it required Lando’s expertise about the rigged Falcon to make a call and get Chewie’s message (ch. 29, p. 275). Thus, Leia should have been rather surprised that the four of them were aware of her situation at all.

Then, Luke’s answer is even more inscrutable. He claims that the ship’s breakdown was the reason for taking a shortcut through the sewer. That causality is wrong: they opted for the sewer because going through the front door would have been much more dangerous (ch. 33, p. 308). Side note: Another incomprehensible thing here is that initially it was Luke who said he had an idea about how to proceed with the rescue mission (ch. 31, p. 302), but now it was Dash who came up with the sewer approach while Luke did not drop the slightest hint at the idea he had claimed to have (the story is full of such puzzling issues).

So, why did Luke associate the ship’s breakdown with the sewer walk? Did I miss something here or was Luke suffering from too much adrenaline and just couldn’t think straight? Maybe, he only tried to seize the opportunity and made that false statement to tease Lando. But there are two counter-arguments against that theory: (1) by now, Luke is the calm and stoic Jedi Knight we know from Return of the Jedi, who probably would not revert to such an infantile joke, and (2) Lando is smart enough to grasp Luke’s intention and would have called out Luke on his faulty comment (especially in front of his crush Leia) instead of clumsily defending himself.

Lando’s reply raises another question. He talks about "Han’s modification" and presumably refers to the escape incident where the Falcon was not able to perform the jump into hyperspace (ch. 25, p. 234). Within a couple of minutes, Lando was able to fix the hyperdrive with a jumper bypass (ch. 25, p. 236) and the Falcon successfully leaped into hyperspace (ch. 27, p. 251). So, why did Luke say that "the ship broke down" when only some specific element of the ship did not work (apart from the hyperdrive, everything else was still intact). In my understanding, an utter breakdown is not the same as a malfunctioning device. Hence, why did Luke choose that strange wording?

Any ideas about all these issues?