Secured loans authorized by ORS § 327.430 shall be repaid in semiannual, quarterly or monthly installments, as may mutually be agreed upon between the borrower and the Department of State Lands, and the installments shall aggregate each year an amount equal to one year’s interest on the original principal of the loan plus an additional two percent of the original principal sum, except as provided in ORS § 327.425. Of the installment so paid each year, the amount at the specified interest rate on the principal remaining unpaid shall be credited as interest and the balance credited to reduction of the loan principal. Borrowers from the fund shall have the right to make payments in excess of the amounts of such installments, and the further right at any time to pay off such loans in part or full with interest to payment dates. [Amended by 1965 c.532 § 7]