As a rank-n-file labor worker, it's probably impossible to 'spike' the pension. There would have to be specific language in the contract. For me and my contract there is language that allows me to build up sick leave and use it as service credit towards retirement. I get 12 days of sick leave a year. 8 hours a day. Over a 30 year career, that could be up to a year's worth a service credit. Under the 2@55
program, that would add 2% to the pension. So a pension that paid out $3000 a month could have another $60 a month if a person wasn't sick often. I'd hardly call that spiking though. (I don't know anyone that saves up that much sick leave anyways...)
More likely, it's salary people who don't record sick leave but just take the day under the auspices of their salaried position. Labor is hourly and every hour is documented.
Overtime isn't part of any PERS retirement pension calculation I know of. Buying time back is, but the employee funds that 100%.
In any case, where I work, the labor cost is 2% of the annual budget. As I was once told during a contract negotiation by the management, "it's chump change, we could double it and not feel the effect. However, you are not worth it."