I would go with the first -- present tense.
Interested in Language
If I want to ask the vendor during guarantee period of something I want to buy in future and want him to do certain things, so can I put it in present simple tense like :
"During this period of guarantee, if the system becomes defective or any malfunction occurs "
or like this:
" During this period of guarantee, if the system became defective or any malfunction occurred "
I would too, but if speaking to the vendor, I wouldn't regard the second as wrong. If the vendor put it in writing, the second would look strange.