As you're obviously aware the business is seasonal, and it's easy to find jobs now as shops need to ramp up for the season. It's impossible to predict whether any business will keep you year round, and maybe the best bet is to ask current employees what happened last year.

On the bright side, most better shops, regardless of size, feel they make an investment in their mechanics and don't really see good productivity for a while, and so are loathe to lay off good ones, though they may dut your hours seasonally.

Also bigger shops are more likely to cut hours or lay off based on seniority (Last in, First out) while a smaller shop will base decisions on performance. One dealer I've known for years celebrated independence day in September, because that's when he got the freedom to let go of marginal employees that he needed to keep all Spring and Summer, because he was too busy to cut staff.

In any case you cannot make a reasoned judgment working from the general to the specific, so you need to get whatever info you can, but ultimately it's a roll of the dice. Regardless of where you work, an employee who shows up on time daily, is honest & willing to learn the company way, and turns out good work is a prize and rarely gets let go.